• Dexuan Cui's avatar
    x86/kvmclock: Fix Hyper-V Isolated VM's boot issue when vCPUs > 64 · 92e68cc5
    Dexuan Cui authored
    When Linux runs as an Isolated VM on Hyper-V, it supports AMD SEV-SNP
    but it's partially enlightened, i.e. cc_platform_has(
    CC_ATTR_GUEST_MEM_ENCRYPT) is true but sev_active() is false.
    
    Commit 4d96f910 per se is good, but with it now
    kvm_setup_vsyscall_timeinfo() -> kvmclock_init_mem() calls
    set_memory_decrypted(), and later gets stuck when trying to zere out
    the pages pointed by 'hvclock_mem', if Linux runs as an Isolated VM on
    Hyper-V. The cause is that here now the Linux VM should no longer access
    the original guest physical addrss (GPA); instead the VM should do
    memremap() and access the original GPA + ms_hyperv.shared_gpa_boundary:
    see the example code in drivers/hv/connection.c: vmbus_connect() or
    drivers/hv/ring_buffer.c: hv_ringbuffer_init(). If the VM tries to
    access the original GPA, it keepts getting injected a fault by Hyper-V
    and gets stuck there.
    
    Here the issue happens only when the VM has >=65 vCPUs, because the
    global static array hv_clock_boot[] can hold 64 "struct
    pvclock_vsyscall_time_info" (the sizeof of the struct is 64 bytes), so
    kvmclock_init_mem() only allocates memory in the case of vCPUs > 64.
    
    Since the 'hvclock_mem' pages are only useful when the kvm clock is
    supported by the underlying hypervisor, fix the issue by returning
    early when Linux VM runs on Hyper-V, which doesn't support kvm clock.
    
    Fixes: 4d96f910 ("x86/sev: Replace occurrences of sev_active() with cc_platform_has()")
    Tested-by: default avatarAndrea Parri (Microsoft) <parri.andrea@gmail.com>
    Signed-off-by: default avatarAndrea Parri (Microsoft) <parri.andrea@gmail.com>
    Signed-off-by: default avatarDexuan Cui <decui@microsoft.com>
    Message-Id: <20220225084600.17817-1-decui@microsoft.com>
    Signed-off-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
    92e68cc5
kvmclock.c 8.5 KB