- 15 Aug, 2018 40 commits
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Konrad Rzeszutek Wilk authored
commit 390d975e upstream If the L1D flush module parameter is set to 'always' and the IA32_FLUSH_CMD MSR is available, optimize the VMENTER code with the MSR save list. Signed-off-by:
Konrad Rzeszutek Wilk <konrad.wilk@oracle.com> Signed-off-by:
Thomas Gleixner <tglx@linutronix.de> Signed-off-by:
David Woodhouse <dwmw@amazon.co.uk> Signed-off-by:
Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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Konrad Rzeszutek Wilk authored
commit 989e3992 upstream The IA32_FLUSH_CMD MSR needs only to be written on VMENTER. Extend add_atomic_switch_msr() with an entry_only parameter to allow storing the MSR only in the guest (ENTRY) MSR array. Signed-off-by:
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Konrad Rzeszutek Wilk authored
commit 31907093 upstream This allows to load a different number of MSRs depending on the context: VMEXIT or VMENTER. Signed-off-by:
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Konrad Rzeszutek Wilk authored
commit ca83b4a7 upstream .. to help find the MSR on either the guest or host MSR list. Signed-off-by:
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Konrad Rzeszutek Wilk authored
commit 33966dd6 upstream There is no semantic change but this change allows an unbalanced amount of MSRs to be loaded on VMEXIT and VMENTER, i.e. the number of MSRs to save or restore on VMEXIT or VMENTER may be different. Signed-off-by:
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Jim Mattson authored
Commit 83bafef1 upstream When L0 establishes (or removes) an MSR entry in the VM-entry or VM-exit MSR load lists, the change should affect the dormant VMCS as well as the current VMCS. Moreover, the vmcs02 MSR-load addresses should be initialized. [ dwmw2: Pulled in to 4.9 backports for L1TF ] Signed-off-by:
Jim Mattson <jmattson@google.com> Signed-off-by:
Radim Krčmář <rkrcmar@redhat.com> Signed-off-by:
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Paolo Bonzini authored
commit c595ceee upstream Add the logic for flushing L1D on VMENTER. The flush depends on the static key being enabled and the new l1tf_flush_l1d flag being set. The flags is set: - Always, if the flush module parameter is 'always' - Conditionally at: - Entry to vcpu_run(), i.e. after executing user space - From the sched_in notifier, i.e. when switching to a vCPU thread. - From vmexit handlers which are considered unsafe, i.e. where sensitive data can be brought into L1D: - The emulator, which could be a good target for other speculative execution-based threats, - The MMU, which can bring host page tables in the L1 cache. - External interrupts - Nested operations that require the MMU (see above). That is vmptrld, vmptrst, vmclear,vmwrite,vmread. - When handling invept,invvpid [ tglx: Split out from combo patch and reduced to a single flag ] [ dwmw2: Backported to 4.9, set l1tf_flush_l1d in svm/vmx code ] Signed-off-by:
Paolo Bonzini <pbonzini@redhat.com> Signed-off-by:
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Paolo Bonzini authored
commit 3fa045be upstream 336996-Speculative-Execution-Side-Channel-Mitigations.pdf defines a new MSR (IA32_FLUSH_CMD aka 0x10B) which has similar write-only semantics to other MSRs defined in the document. The semantics of this MSR is to allow "finer granularity invalidation of caching structures than existing mechanisms like WBINVD. It will writeback and invalidate the L1 data cache, including all cachelines brought in by preceding instructions, without invalidating all caches (eg. L2 or LLC). Some processors may also invalidate the first level level instruction cache on a L1D_FLUSH command. The L1 data and instruction caches may be shared across the logical processors of a core." Use it instead of the loop based L1 flush algorithm. A copy of this document is available at https://bugzilla.kernel.org/show_bug.cgi?id=199511 [ tglx: Avoid allocating pages when the MSR is available ] Signed-off-by:
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Paolo Bonzini authored
commit a47dd5f0 upstream To mitigate the L1 Terminal Fault vulnerability it's required to flush L1D on VMENTER to prevent rogue guests from snooping host memory. CPUs will have a new control MSR via a microcode update to flush L1D with a single MSR write, but in the absence of microcode a fallback to a software based flush algorithm is required. Add a software flush loop which is based on code from Intel. [ tglx: Split out from combo patch ] [ bpetkov: Polish the asm code ] Signed-off-by:
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Konrad Rzeszutek Wilk authored
commit a399477e upstream Add a mitigation mode parameter "vmentry_l1d_flush" for CVE-2018-3620, aka L1 terminal fault. The valid arguments are: - "always" L1D cache flush on every VMENTER. - "cond" Conditional L1D cache flush, explained below - "never" Disable the L1D cache flush mitigation "cond" is trying to avoid L1D cache flushes on VMENTER if the code executed between VMEXIT and VMENTER is considered safe, i.e. is not bringing any interesting information into L1D which might exploited. [ tglx: Split out from a larger patch ] Signed-off-by:
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Konrad Rzeszutek Wilk authored
commit 26acfb66 upstream If the L1TF CPU bug is present we allow the KVM module to be loaded as the major of users that use Linux and KVM have trusted guests and do not want a broken setup. Cloud vendors are the ones that are uncomfortable with CVE 2018-3620 and as such they are the ones that should set nosmt to one. Setting 'nosmt' means that the system administrator also needs to disable SMT (Hyper-threading) in the BIOS, or via the 'nosmt' command line parameter, or via the /sys/devices/system/cpu/smt/control. See commit 05736e4a ("cpu/hotplug: Provide knobs to control SMT"). Other mitigations are to use task affinity, cpu sets, interrupt binding, etc - anything to make sure that _only_ the same guests vCPUs are running on sibling threads. Signed-off-by:
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Thomas Gleixner authored
commit 0cc3cd21 upstream Due to the way Machine Check Exceptions work on X86 hyperthreads it's required to boot up _all_ logical cores at least once in order to set the CR4.MCE bit. So instead of ignoring the sibling threads right away, let them boot up once so they can configure themselves. After they came out of the initial boot stage check whether its a "secondary" sibling and cancel the operation which puts the CPU back into offline state. [dwmw2: Backport to 4.9] Reported-by:
Dave Hansen <dave.hansen@intel.com> Signed-off-by:
Tony Luck <tony.luck@intel.com> Signed-off-by:
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Thomas Gleixner authored
commit 506a66f3 upstream Dave Hansen reported, that it's outright dangerous to keep SMT siblings disabled completely so they are stuck in the BIOS and wait for SIPI. The reason is that Machine Check Exceptions are broadcasted to siblings and the soft disabled sibling has CR4.MCE = 0. If a MCE is delivered to a logical core with CR4.MCE = 0, it asserts IERR#, which shuts down or reboots the machine. The MCE chapter in the SDM contains the following blurb: Because the logical processors within a physical package are tightly coupled with respect to shared hardware resources, both logical processors are notified of machine check errors that occur within a given physical processor. If machine-check exceptions are enabled when a fatal error is reported, all the logical processors within a physical package are dispatched to the machine-check exception handler. If machine-check exceptions are disabled, the logical processors enter the shutdown state and assert the IERR# signal. When enabling machine-check exceptions, the MCE flag in control register CR4 should be set for each logical processor. Reverting the commit which ignores siblings at enumeration time solves only half of the problem. The core cpuhotplug logic needs to be adjusted as well. This thoughtful engineered mechanism also turns the boot process on all Intel HT enabled systems into a MCE lottery. MCE is enabled on the boot CPU before the secondary CPUs are brought up. Depending on the number of physical cores the window in which this situation can happen is smaller or larger. On a HSW-EX it's about 750ms: MCE is enabled on the boot CPU: [ 0.244017] mce: CPU supports 22 MCE banks The corresponding sibling #72 boots: [ 1.008005] .... node #0, CPUs: #72 That means if an MCE hits on physical core 0 (logical CPUs 0 and 72) between these two points the machine is going to shutdown. At least it's a known safe state. It's obvious that the early boot can be hit by an MCE as well and then runs into the same situation because MCEs are not yet enabled on the boot CPU. But after enabling them on the boot CPU, it does not make any sense to prevent the kernel from recovering. Adjust the nosmt kernel parameter documentation as well. Reverts: 2207def7 ("x86/apic: Ignore secondary threads if nosmt=force") Reported-by:
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Michal Hocko authored
commit e14d7dfb upstream Jan has noticed that pte_pfn and co. resp. pfn_pte are incorrect for CONFIG_PAE because phys_addr_t is wider than unsigned long and so the pte_val reps. shift left would get truncated. Fix this up by using proper types. [dwmw2: Backport to 4.9] Fixes: 6b28baca ("x86/speculation/l1tf: Protect PROT_NONE PTEs against speculation") Reported-by:
Jan Beulich <JBeulich@suse.com> Signed-off-by:
Michal Hocko <mhocko@suse.com> Signed-off-by:
Vlastimil Babka <vbabka@suse.cz> Signed-off-by:
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Vlastimil Babka authored
commit 0d0f6249 upstream The PAE 3-level paging code currently doesn't mitigate L1TF by flipping the offset bits, and uses the high PTE word, thus bits 32-36 for type, 37-63 for offset. The lower word is zeroed, thus systems with less than 4GB memory are safe. With 4GB to 128GB the swap type selects the memory locations vulnerable to L1TF; with even more memory, also the swap offfset influences the address. This might be a problem with 32bit PAE guests running on large 64bit hosts. By continuing to keep the whole swap entry in either high or low 32bit word of PTE we would limit the swap size too much. Thus this patch uses the whole PAE PTE with the same layout as the 64bit version does. The macros just become a bit tricky since they assume the arch-dependent swp_entry_t to be 32bit. Signed-off-by:
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Borislav Petkov authored
commit 7ce2f039 upstream The TOPOEXT reenablement is a workaround for broken BIOSen which didn't enable the CPUID bit. amd_get_topology_early(), however, relies on that bit being set so that it can read out the CPUID leaf and set smp_num_siblings properly. Move the reenablement up to early_init_amd(). While at it, simplify amd_get_topology_early(). [dwmw2: Backport to 4.9] Signed-off-by:
Borislav Petkov <bp@suse.de> Signed-off-by:
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Konrad Rzeszutek Wilk authored
commit 11e34e64 upstream 336996-Speculative-Execution-Side-Channel-Mitigations.pdf defines a new MSR (IA32_FLUSH_CMD) which is detected by CPUID.7.EDX[28]=1 bit being set. This new MSR "gives software a way to invalidate structures with finer granularity than other architectual methods like WBINVD." A copy of this document is available at https://bugzilla.kernel.org/show_bug.cgi?id=199511Signed-off-by:
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Vlastimil Babka authored
commit 1a7ed1ba upstream The previous patch has limited swap file size so that large offsets cannot clear bits above MAX_PA/2 in the pte and interfere with L1TF mitigation. It assumed that offsets are encoded starting with bit 12, same as pfn. But on x86_64, offsets are encoded starting with bit 9. Thus the limit can be raised by 3 bits. That means 16TB with 42bit MAX_PA and 256TB with 46bit MAX_PA. Fixes: 377eeaa8 ("x86/speculation/l1tf: Limit swap file size to MAX_PA/2") Signed-off-by:
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Thomas Gleixner authored
commit 2207def7 upstream nosmt on the kernel command line merely prevents the onlining of the secondary SMT siblings. nosmt=force makes the APIC detection code ignore the secondary SMT siblings completely, so they even do not show up as possible CPUs. That reduces the amount of memory allocations for per cpu variables and saves other resources from being allocated too large. This is not fully equivalent to disabling SMT in the BIOS because the low level SMT enabling in the BIOS can result in partitioning of resources between the siblings, which is not undone by just ignoring them. Some CPUs can use the full resources when their sibling is not onlined, but this is depending on the CPU family and model and it's not well documented whether this applies to all partitioned resources. That means depending on the workload disabling SMT in the BIOS might result in better performance. Linus analysis of the Intel manual: The intel optimization manual is not very clear on what the partitioning rules are. I find: "In general, the buffers for staging instructions between major pipe stages are partitioned. These buffers include µop queues after the execution trace cache, the queues after the register rename stage, the reorder buffer which stages instructions for retirement, and the load and store buffers. In the case of load and store buffers, partitioning also provided an easier implementation to maintain memory ordering for each logical processor and detect memory ordering violations" but some of that partitioning may be relaxed if the HT thread is "not active": "In Intel microarchitecture code name Sandy Bridge, the micro-op queue is statically partitioned to provide 28 entries for each logical processor, irrespective of software executing in single thread or multiple threads. If one logical processor is not active in Intel microarchitecture code name Ivy Bridge, then a single thread executing on that processor core can use the 56 entries in the micro-op queue" but I do not know what "not active" means, and how dynamic it is. Some of that partitioning may be entirely static and depend on the early BIOS disabling of HT, and even if we park the cores, the resources will just be wasted. Signed-off-by:
Ingo Molnar <mingo@kernel.org> Signed-off-by:
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Thomas Gleixner authored
commit 1e1d7e25 upstream To support force disabling of SMT it's required to know the number of thread siblings early. amd_get_topology() cannot be called before the APIC driver is selected, so split out the part which initializes smp_num_siblings and invoke it from amd_early_init(). [dwmw2: Backport to 4.9] Signed-off-by:
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Borislav Petkov authored
commit 119bff8a upstream Old code used to check whether CPUID ext max level is >= 0x80000008 because that last leaf contains the number of cores of the physical CPU. The three functions called there now do not depend on that leaf anymore so the check can go. Signed-off-by:
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Thomas Gleixner authored
commit 1910ad56 upstream Make use of the new early detection function to initialize smp_num_siblings on the boot cpu before the MP-Table or ACPI/MADT scan happens. That's required for force disabling SMT. Signed-off-by:
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Thomas Gleixner authored
commit 95f3d39c upstream To support force disabling of SMT it's required to know the number of thread siblings early. detect_extended_topology() cannot be called before the APIC driver is selected, so split out the part which initializes smp_num_siblings. Signed-off-by:
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Thomas Gleixner authored
commit 545401f4 upstream To support force disabling of SMT it's required to know the number of thread siblings early. detect_ht() cannot be called before the APIC driver is selected, so split out the part which initializes smp_num_siblings. Signed-off-by:
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Thomas Gleixner authored
commit 44ca36de upstream Real 32bit AMD CPUs do not have SMT and the only value of the call was to reach the magic printout which got removed. Signed-off-by:
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Thomas Gleixner authored
commit 55e6d279 upstream The value of this printout is dubious at best and there is no point in having it in two different places along with convoluted ways to reach it. Remove it completely. Signed-off-by:
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Thomas Gleixner authored
commit 05736e4a upstream Provide a command line and a sysfs knob to control SMT. The command line options are: 'nosmt': Enumerate secondary threads, but do not online them 'nosmt=force': Ignore secondary threads completely during enumeration via MP table and ACPI/MADT. The sysfs control file has the following states (read/write): 'on': SMT is enabled. Secondary threads can be freely onlined 'off': SMT is disabled. Secondary threads, even if enumerated cannot be onlined 'forceoff': SMT is permanentely disabled. Writes to the control file are rejected. 'notsupported': SMT is not supported by the CPU The command line option 'nosmt' sets the sysfs control to 'off'. This can be changed to 'on' to reenable SMT during runtime. The command line option 'nosmt=force' sets the sysfs control to 'forceoff'. This cannot be changed during runtime. When SMT is 'on' and the control file is changed to 'off' then all online secondary threads are offlined and attempts to online a secondary thread later on are rejected. When SMT is 'off' and the control file is changed to 'on' then secondary threads can be onlined again. The 'off' -> 'on' transition does not automatically online the secondary threads. When the control file is set to 'forceoff', the behaviour is the same as setting it to 'off', but the operation is irreversible and later writes to the control file are rejected. When the control status is 'notsupported' then writes to the control file are rejected. Signed-off-by:
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Thomas Gleixner authored
commit cc1fe215 upstream Split out the inner workings of do_cpu_down() to allow reuse of that function for the upcoming SMT disabling mechanism. No functional change. Signed-off-by:
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Thomas Gleixner authored
commit c4de6569 upstream The asymmetry caused a warning to trigger if the bootup was stopped in state CPUHP_AP_ONLINE_IDLE. The warning no longer triggers as kthread_park() can now be invoked on already or still parked threads. But there is still no reason to have this be asymmetric. Signed-off-by:
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Thomas Gleixner authored
commit f048c399 upstream Provide information whether SMT is supoorted by the CPUs. Preparatory patch for SMT control mechanism. Suggested-by:
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Thomas Gleixner authored
commit 6a4d2657 upstream If the CPU is supporting SMT then the primary thread can be found by checking the lower APIC ID bits for zero. smp_num_siblings is used to build the mask for the APIC ID bits which need to be taken into account. This uses the MPTABLE or ACPI/MADT supplied APIC ID, which can be different than the initial APIC ID in CPUID. But according to AMD the lower bits have to be consistent. Intel gave a tentative confirmation as well. Preparatory patch to support disabling SMT at boot/runtime. Signed-off-by:
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Konrad Rzeszutek Wilk authored
commit 56563f53 upstream The pr_warn in l1tf_select_mitigation would have used the prior pr_fmt which was defined as "Spectre V2 : ". Move the function to be past SSBD and also define the pr_fmt. Fixes: 17dbca11 ("x86/speculation/l1tf: Add sysfs reporting for l1tf") Signed-off-by:
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Andi Kleen authored
commit 377eeaa8 upstream For the L1TF workaround its necessary to limit the swap file size to below MAX_PA/2, so that the higher bits of the swap offset inverted never point to valid memory. Add a mechanism for the architecture to override the swap file size check in swapfile.c and add a x86 specific max swapfile check function that enforces that limit. The check is only enabled if the CPU is vulnerable to L1TF. In VMs with 42bit MAX_PA the typical limit is 2TB now, on a native system with 46bit PA it is 32TB. The limit is only per individual swap file, so it's always possible to exceed these limits with multiple swap files or partitions. Signed-off-by:
Andi Kleen <ak@linux.intel.com> Signed-off-by:
Josh Poimboeuf <jpoimboe@redhat.com> Acked-by:
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Andi Kleen authored
commit 42e4089c upstream For L1TF PROT_NONE mappings are protected by inverting the PFN in the page table entry. This sets the high bits in the CPU's address space, thus making sure to point to not point an unmapped entry to valid cached memory. Some server system BIOSes put the MMIO mappings high up in the physical address space. If such an high mapping was mapped to unprivileged users they could attack low memory by setting such a mapping to PROT_NONE. This could happen through a special device driver which is not access protected. Normal /dev/mem is of course access protected. To avoid this forbid PROT_NONE mappings or mprotect for high MMIO mappings. Valid page mappings are allowed because the system is then unsafe anyways. It's not expected that users commonly use PROT_NONE on MMIO. But to minimize any impact this is only enforced if the mapping actually refers to a high MMIO address (defined as the MAX_PA-1 bit being set), and also skip the check for root. For mmaps this is straight forward and can be handled in vm_insert_pfn and in remap_pfn_range(). For mprotect it's a bit trickier. At the point where the actual PTEs are accessed a lot of state has been changed and it would be difficult to undo on an error. Since this is a uncommon case use a separate early page talk walk pass for MMIO PROT_NONE mappings that checks for this condition early. For non MMIO and non PROT_NONE there are no changes. [dwmw2: Backport to 4.9] Signed-off-by:
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Andi Kleen authored
commit 17dbca11 upstream L1TF core kernel workarounds are cheap and normally always enabled, However they still should be reported in sysfs if the system is vulnerable or mitigated. Add the necessary CPU feature/bug bits. - Extend the existing checks for Meltdowns to determine if the system is vulnerable. All CPUs which are not vulnerable to Meltdown are also not vulnerable to L1TF - Check for 32bit non PAE and emit a warning as there is no practical way for mitigation due to the limited physical address bits - If the system has more than MAX_PA/2 physical memory the invert page workarounds don't protect the system against the L1TF attack anymore, because an inverted physical address will also point to valid memory. Print a warning in this case and report that the system is vulnerable. Add a function which returns the PFN limit for the L1TF mitigation, which will be used in follow up patches for sanity and range checks. [ tglx: Renamed the CPU feature bit to L1TF_PTEINV ] [ dwmw2: Backport to 4.9 (cpufeatures.h, E820) ] Signed-off-by:
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Andi Kleen authored
commit 10a70416 upstream The L1TF workaround doesn't make any attempt to mitigate speculate accesses to the first physical page for zeroed PTEs. Normally it only contains some data from the early real mode BIOS. It's not entirely clear that the first page is reserved in all configurations, so add an extra reservation call to make sure it is really reserved. In most configurations (e.g. with the standard reservations) it's likely a nop. Signed-off-by:
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Andi Kleen authored
commit 6b28baca upstream When PTEs are set to PROT_NONE the kernel just clears the Present bit and preserves the PFN, which creates attack surface for L1TF speculation speculation attacks. This is important inside guests, because L1TF speculation bypasses physical page remapping. While the host has its own migitations preventing leaking data from other VMs into the guest, this would still risk leaking the wrong page inside the current guest. This uses the same technique as Linus' swap entry patch: while an entry is is in PROTNONE state invert the complete PFN part part of it. This ensures that the the highest bit will point to non existing memory. The invert is done by pte/pmd_modify and pfn/pmd/pud_pte for PROTNONE and pte/pmd/pud_pfn undo it. This assume that no code path touches the PFN part of a PTE directly without using these primitives. This doesn't handle the case that MMIO is on the top of the CPU physical memory. If such an MMIO region was exposed by an unpriviledged driver for mmap it would be possible to attack some real memory. However this situation is all rather unlikely. For 32bit non PAE the inversion is not done because there are really not enough bits to protect anything. Q: Why does the guest need to be protected when the HyperVisor already has L1TF mitigations? A: Here's an example: Physical pages 1 2 get mapped into a guest as GPA 1 -> PA 2 GPA 2 -> PA 1 through EPT. The L1TF speculation ignores the EPT remapping. Now the guest kernel maps GPA 1 to process A and GPA 2 to process B, and they belong to different users and should be isolated. A sets the GPA 1 PA 2 PTE to PROT_NONE to bypass the EPT remapping and gets read access to the underlying physical page. Which in this case points to PA 2, so it can read process B's data, if it happened to be in L1, so isolation inside the guest is broken. There's nothing the hypervisor can do about this. This mitigation has to be done in the guest itself. [ tglx: Massaged changelog ] [ dwmw2: backported to 4.9 ] Signed-off-by:
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Linus Torvalds authored
commit 2f22b4cd upstream With L1 terminal fault the CPU speculates into unmapped PTEs, and resulting side effects allow to read the memory the PTE is pointing too, if its values are still in the L1 cache. For swapped out pages Linux uses unmapped PTEs and stores a swap entry into them. To protect against L1TF it must be ensured that the swap entry is not pointing to valid memory, which requires setting higher bits (between bit 36 and bit 45) that are inside the CPUs physical address space, but outside any real memory. To do this invert the offset to make sure the higher bits are always set, as long as the swap file is not too big. Note there is no workaround for 32bit !PAE, or on systems which have more than MAX_PA/2 worth of memory. The later case is very unlikely to happen on real systems. [AK: updated description and minor tweaks by. Split out from the original patch ] Signed-off-by:
Linus Torvalds <torvalds@linux-foundation.org> Signed-off-by:
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Linus Torvalds authored
commit bcd11afa upstream If pages are swapped out, the swap entry is stored in the corresponding PTE, which has the Present bit cleared. CPUs vulnerable to L1TF speculate on PTE entries which have the present bit set and would treat the swap entry as phsyical address (PFN). To mitigate that the upper bits of the PTE must be set so the PTE points to non existent memory. The swap entry stores the type and the offset of a swapped out page in the PTE. type is stored in bit 9-13 and offset in bit 14-63. The hardware ignores the bits beyond the phsyical address space limit, so to make the mitigation effective its required to start 'offset' at the lowest possible bit so that even large swap offsets do not reach into the physical address space limit bits. Move offset to bit 9-58 and type to bit 59-63 which are the bits that hardware generally doesn't care about. That, in turn, means that if you on desktop chip with only 40 bits of physical addressing, now that the offset starts at bit 9, there needs to be 30 bits of offset actually *in use* until bit 39 ends up being set, which means when inverted it will again point into existing memory. So that's 4 terabyte of swap space (because the offset is counted in pages, so 30 bits of offset is 42 bits of actual coverage). With bigger physical addressing, that obviously grows further, until the limit of the offset is hit (at 50 bits of offset - 62 bits of actual swap file coverage). This is a preparatory change for the actual swap entry inversion to protect against L1TF. [ AK: Updated description and minor tweaks. Split into two parts ] [ tglx: Massaged changelog ] Signed-off-by:
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Naoya Horiguchi authored
commit eee4818b upstream _PAGE_PSE is used to distinguish between a truly non-present (_PAGE_PRESENT=0) PMD, and a PMD which is undergoing a THP split and should be treated as present. But _PAGE_SWP_SOFT_DIRTY currently uses the _PAGE_PSE bit, which would cause confusion between one of those PMDs undergoing a THP split, and a soft-dirty PMD. Dropping _PAGE_PSE check in pmd_present() does not work well, because it can hurt optimization of tlb handling in thp split. Thus, we need to move the bit. In the current kernel, bits 1-4 are not used in non-present format since commit 00839ee3 ("x86/mm: Move swap offset/type up in PTE to work around erratum"). So let's move _PAGE_SWP_SOFT_DIRTY to bit 1. Bit 7 is used as reserved (always clear), so please don't use it for other purpose. [dwmw2: Pulled in to 4.9 backport to support L1TF changes] Link: http://lkml.kernel.org/r/20170717193955.20207-3-zi.yan@sent.comSigned-off-by:
Naoya Horiguchi <n-horiguchi@ah.jp.nec.com> Signed-off-by:
Zi Yan <zi.yan@cs.rutgers.edu> Acked-by:
Andrew Morton <akpm@linux-foundation.org> Signed-off-by:
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