From: Ramakrishna Saripalli <rk.saripa...@amd.com>
Certain AMD processors feature a new technology called Predictive Store
Forwarding (PSF).
PSF is a micro-architectural optimization designed to improve the
performance of code execution by predicting dependencies between
loads and stores.
Incorrect PSF predictions can occur due to two reasons.
- It is possible that the load/store pair may have had dependency for
a while but the dependency has stopped because the address in the
load/store pair has changed.
- Second source of incorrect PSF prediction can occur because of an alias
in the PSF predictor structure stored in the microarchitectural state.
PSF predictor tracks load/store pair based on portions of instruction
pointer. It is possible that a load/store pair which does have a
dependency may be aliased by another load/store pair which does not have
the same dependency. This can result in incorrect speculation.
Software may be able to detect this aliasing and perform side-channel
attacks.
These features are being introduced to support mitigation from these attacks.
All CPUs that implement PSF provide one bit to disable this feature.
If the bit to disable this feature is available, it means that the CPU
implements PSF feature and is therefore vulnerable to PSF risks.
The bits that are introduced
X86_FEATURE_AMD_PSFD: CPUID_Fn80000008_EBX[28] ("PSF disable")
If this bit is 1, CPU implements PSF and PSF mitigation is
supported.
X86_FEATURE_PSFD: Generic Linux feature to indicate the CPU supports
controls to mitigate PSF.
X86_FEATURE_PSFD is set if and only if X86_FEATURE_AMD_PSFD
is set
X86_BUG_PSF: Generic Linux feature to indicate that the CPU is affected
by the PSF feature.
Signed-off-by: Ramakrishna Saripalli<rk.saripa...@amd.com>
---
arch/x86/include/asm/cpufeatures.h | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)
diff --git a/arch/x86/include/asm/cpufeatures.h
b/arch/x86/include/asm/cpufeatures.h
index cc96e26d69f7..21e7f8d0d7d9 100644
--- a/arch/x86/include/asm/cpufeatures.h
+++ b/arch/x86/include/asm/cpufeatures.h
@@ -201,7 +201,7 @@
#define X86_FEATURE_INVPCID_SINGLE ( 7*32+ 7) /* Effectively INVPCID &&
CR4.PCIDE=1 */
#define X86_FEATURE_HW_PSTATE ( 7*32+ 8) /* AMD HW-PState */
#define X86_FEATURE_PROC_FEEDBACK ( 7*32+ 9) /* AMD ProcFeedbackInterface
*/
-/* FREE! ( 7*32+10) */
+#define X86_FEATURE_PSFD ( 7*32+10) /* Predictive Store Forward
Disable */
#define X86_FEATURE_PTI ( 7*32+11) /* Kernel Page Table
Isolation enabled */
#define X86_FEATURE_RETPOLINE ( 7*32+12) /* "" Generic Retpoline
mitigation for Spectre variant 2 */
#define X86_FEATURE_RETPOLINE_AMD ( 7*32+13) /* "" AMD Retpoline
mitigation for Spectre variant 2 */
@@ -309,6 +309,7 @@
#define X86_FEATURE_AMD_SSBD (13*32+24) /* "" Speculative Store
Bypass Disable */
#define X86_FEATURE_VIRT_SSBD (13*32+25) /* Virtualized Speculative
Store Bypass Disable */
#define X86_FEATURE_AMD_SSB_NO (13*32+26) /* "" Speculative Store
Bypass is fixed in hardware. */
+#define X86_FEATURE_AMD_PSFD (13*32+28) /* "" Predictive Store
Forward Disable */
/* Thermal and Power Management Leaf, CPUID level 0x00000006 (EAX), word 14 */
#define X86_FEATURE_DTHERM (14*32+ 0) /* Digital Thermal Sensor */
@@ -428,5 +429,6 @@
#define X86_BUG_TAA X86_BUG(22) /* CPU is affected by TSX
Async Abort(TAA) */
#define X86_BUG_ITLB_MULTIHIT X86_BUG(23) /* CPU may incur MCE during
certain page attribute changes */
#define X86_BUG_SRBDS X86_BUG(24) /* CPU may leak RNG bits if
not mitigated */
+#define X86_BUG_PSF X86_BUG(25) /* CPU is affected by
Predictive Store Forwarding attack */
#endif /* _ASM_X86_CPUFEATURES_H */
--
2.25.1
