x86/speculation: Add virtualized speculative store bypass disable support

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>

diff --git a/arch/x86/include/asm/cpufeatures.h b/arch/x86/include/asm/cpufeatures.h
index 8099be4..fb00a2f 100644 (file)
--- a/arch/x86/include/asm/cpufeatures.h
+++ b/arch/x86/include/asm/cpufeatures.h
@@ -282,6 +282,7 @@
 #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 */

diff --git a/arch/x86/include/asm/msr-index.h b/arch/x86/include/asm/msr-index.h
index 0da3ca2..562414d 100644 (file)
--- a/arch/x86/include/asm/msr-index.h
+++ b/arch/x86/include/asm/msr-index.h
@@ -347,6 +347,8 @@
 #define MSR_AMD64_SEV_ENABLED_BIT      0
 #define MSR_AMD64_SEV_ENABLED          BIT_ULL(MSR_AMD64_SEV_ENABLED_BIT)
 
+#define MSR_AMD64_VIRT_SPEC_CTRL       0xc001011f
+
 /* Fam 17h MSRs */
 #define MSR_F17H_IRPERF                        0xc00000e9
 

diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
index d3afd38..82422a0 100644 (file)
--- a/arch/x86/kernel/cpu/bugs.c
+++ b/arch/x86/kernel/cpu/bugs.c
@@ -205,7 +205,9 @@ 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);
 }
 

diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c
index d6fe864..91c3398 100644 (file)
--- a/arch/x86/kernel/process.c
+++ b/arch/x86/kernel/process.c
@@ -388,6 +388,15 @@ 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);
@@ -397,7 +406,9 @@ 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);