x86/speculation: Add virtualized speculative store bypass disable support

commit 11fb0683 upstream

Some AMD processors only support a non-architectural means of enabling
speculative store bypass disable (SSBD).  To allow a simplified view of
this to a guest, an architectural definition has been created through a new
CPUID bit, 0x80000008_EBX[25], and a new MSR, 0xc001011f.  With this, a
hypervisor can virtualize the existence of this definition and provide an
architectural method for using SSBD to a guest.

Add the new CPUID feature, the new MSR and update the existing SSBD
support to use this MSR when present.
Signed-off-by: Tom Lendacky <thomas.lendacky@amd.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Borislav Petkov <bp@suse.de>
Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Srivatsa S. Bhat <srivatsa@csail.mit.edu>
Reviewed-by: Matt Helsley (VMware) <matt.helsley@gmail.com>
Reviewed-by: Alexey Makhalov <amakhalov@vmware.com>
Reviewed-by: Bo Gan <ganb@vmware.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

arch/x86/include/asm/cpufeatures.h

@@ -269,6 +269,7 @@
 #define X86_FEATURE_AMD_IBPB	(13*32+12) /* Indirect Branch Prediction Barrier */
 #define X86_FEATURE_AMD_IBRS	(13*32+14) /* Indirect Branch Restricted Speculation */
 #define X86_FEATURE_AMD_STIBP	(13*32+15) /* Single Thread Indirect Branch Predictors */
+#define X86_FEATURE_VIRT_SSBD	(13*32+25) /* Virtualized Speculative Store Bypass Disable */
 
 /* Thermal and Power Management Leaf, CPUID level 0x00000006 (eax), word 14 */
 #define X86_FEATURE_DTHERM	(14*32+ 0) /* Digital Thermal Sensor */

arch/x86/include/asm/msr-index.h

@@ -328,6 +328,8 @@
 #define MSR_AMD64_IBSOPDATA4		0xc001103d
 #define MSR_AMD64_IBS_REG_COUNT_MAX	8 /* includes MSR_AMD64_IBSBRTARGET */
 
+#define MSR_AMD64_VIRT_SPEC_CTRL	0xc001011f
+
 /* Fam 16h MSRs */
 #define MSR_F16H_L2I_PERF_CTL		0xc0010230
 #define MSR_F16H_L2I_PERF_CTR		0xc0010231

arch/x86/kernel/cpu/bugs.c

@@ -203,7 +203,9 @@ static void x86_amd_ssb_disable(void)
 {
 	u64 msrval = x86_amd_ls_cfg_base | x86_amd_ls_cfg_ssbd_mask;
 
-	if (boot_cpu_has(X86_FEATURE_LS_CFG_SSBD))
+	if (boot_cpu_has(X86_FEATURE_VIRT_SSBD))
+		wrmsrl(MSR_AMD64_VIRT_SPEC_CTRL, SPEC_CTRL_SSBD);
+	else if (boot_cpu_has(X86_FEATURE_LS_CFG_SSBD))
 		wrmsrl(MSR_AMD64_LS_CFG, msrval);
 }
 

arch/x86/kernel/process.c

@@ -308,6 +308,15 @@ static __always_inline void amd_set_core_ssb_state(unsigned long tifn)
 }
 #endif
 
+static __always_inline void amd_set_ssb_virt_state(unsigned long tifn)
+{
+	/*
+	 * SSBD has the same definition in SPEC_CTRL and VIRT_SPEC_CTRL,
+	 * so ssbd_tif_to_spec_ctrl() just works.
+	 */
+	wrmsrl(MSR_AMD64_VIRT_SPEC_CTRL, ssbd_tif_to_spec_ctrl(tifn));
+}
+
 static __always_inline void intel_set_ssb_state(unsigned long tifn)
 {
 	u64 msr = x86_spec_ctrl_base | ssbd_tif_to_spec_ctrl(tifn);
@@ -317,7 +326,9 @@ static __always_inline void intel_set_ssb_state(unsigned long tifn)
 
 static __always_inline void __speculative_store_bypass_update(unsigned long tifn)
 {
-	if (static_cpu_has(X86_FEATURE_LS_CFG_SSBD))
+	if (static_cpu_has(X86_FEATURE_VIRT_SSBD))
+		amd_set_ssb_virt_state(tifn);
+	else if (static_cpu_has(X86_FEATURE_LS_CFG_SSBD))
 		amd_set_core_ssb_state(tifn);
 	else
 		intel_set_ssb_state(tifn);