Hi,
I was reading the AMD whitepaper on SSBD and noticed that they have added
two new bits in the 8000_0008 CPUID. EBX:
1) Bit[26] - similar to Intel's SSB_NO not needed anymore.
2) Bit[24] - use SPEC_CTRL MSR (0x48) instead of VIRT SPEC_CTRL MSR
(0xC001_011f).
See 124441_AMD64_SpeculativeStoreBypassDisable_Whitepaper_final.pdf
(A copy of this document is available at
https://bugzilla.kernel.org/show_bug.cgi?id=199889)
Being that I don't have the hardware (not even sure if AMD has developed it yet)
I ended up cobbling up a DEBUG patch, the last one - which is well, debug
(see below).
QEMU patches will be sent in another patchset.
arch/x86/include/asm/cpufeatures.h | 2 ++
arch/x86/kernel/cpu/bugs.c | 13 +++++--------
arch/x86/kernel/cpu/common.c | 9 ++++++++-
arch/x86/kvm/cpuid.c | 10 ++++++++--
arch/x86/kvm/svm.c | 8 +++++---
5 files changed, 28 insertions(+), 14 deletions(-)
Konrad Rzeszutek Wilk (3):
x86/bugs: Add AMD's variant of SSB_NO.
x86/bugs: Add AMD's SPEC_CTRL MSR usage
x86/bugs: Switch the selection of mitigation from CPU vendor to CPU features
>From 3d120f90731dae7e9a6f0c941c8bc228ed346baa Mon Sep 17 00:00:00 2001
From: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
Date: Thu, 31 May 2018 20:56:08 -0400
Subject: [PATCH] DEBUG HACK DEBUG
Expose the two various Bits to the guest depending on the module
parameters.
Also show the various hidden flags in the /proc/cpuinfo.
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
---
arch/x86/include/asm/cpufeatures.h | 14 +++++++-------
arch/x86/kvm/cpuid.c | 12 ++++++++++++
arch/x86/kvm/svm.c | 13 -------------
3 files changed, 19 insertions(+), 20 deletions(-)
diff --git a/arch/x86/include/asm/cpufeatures.h b/arch/x86/include/asm/cpufeatures.h
index 5701f5cecd31..05b74564089a 100644
--- a/arch/x86/include/asm/cpufeatures.h
+++ b/arch/x86/include/asm/cpufeatures.h
@@ -206,15 +206,15 @@
#define X86_FEATURE_RETPOLINE_AMD ( 7*32+13) /* "" AMD Retpoline mitigation for Spectre variant 2 */
#define X86_FEATURE_INTEL_PPIN ( 7*32+14) /* Intel Processor Inventory Number */
#define X86_FEATURE_CDP_L2 ( 7*32+15) /* Code and Data Prioritization L2 */
-#define X86_FEATURE_MSR_SPEC_CTRL ( 7*32+16) /* "" MSR SPEC_CTRL is implemented */
+#define X86_FEATURE_MSR_SPEC_CTRL ( 7*32+16) /* MSR SPEC_CTRL is implemented */
#define X86_FEATURE_SSBD ( 7*32+17) /* Speculative Store Bypass Disable */
#define X86_FEATURE_MBA ( 7*32+18) /* Memory Bandwidth Allocation */
#define X86_FEATURE_RSB_CTXSW ( 7*32+19) /* "" Fill RSB on context switches */
#define X86_FEATURE_SEV ( 7*32+20) /* AMD Secure Encrypted Virtualization */
#define X86_FEATURE_USE_IBPB ( 7*32+21) /* "" Indirect Branch Prediction Barrier enabled */
#define X86_FEATURE_USE_IBRS_FW ( 7*32+22) /* "" Use IBRS during runtime firmware calls */
-#define X86_FEATURE_SPEC_STORE_BYPASS_DISABLE ( 7*32+23) /* "" Disable Speculative Store Bypass. */
-#define X86_FEATURE_LS_CFG_SSBD ( 7*32+24) /* "" AMD SSBD implementation via LS_CFG MSR */
+#define X86_FEATURE_SPEC_STORE_BYPASS_DISABLE ( 7*32+23) /* Disable Speculative Store Bypass. */
+#define X86_FEATURE_LS_CFG_SSBD ( 7*32+24) /* AMD SSBD implementation via LS_CFG MSR */
#define X86_FEATURE_IBRS ( 7*32+25) /* Indirect Branch Restricted Speculation */
#define X86_FEATURE_IBPB ( 7*32+26) /* Indirect Branch Prediction Barrier */
#define X86_FEATURE_STIBP ( 7*32+27) /* Single Thread Indirect Branch Predictors */
@@ -279,12 +279,12 @@
#define X86_FEATURE_CLZERO (13*32+ 0) /* CLZERO instruction */
#define X86_FEATURE_IRPERF (13*32+ 1) /* Instructions Retired Count */
#define X86_FEATURE_XSAVEERPTR (13*32+ 2) /* Always save/restore FP error pointers */
-#define X86_FEATURE_AMD_IBPB (13*32+12) /* "" Indirect Branch Prediction Barrier */
+#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_AMD_SSBD (13*32+24) /* "" Speculative Store Bypass Disable */
+#define X86_FEATURE_AMD_STIBP (13*32+15) /* Single Thread Indirect Branch Predictors */
+#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_SSB_NO (13*32+26) /* Speculative Store Bypass is fixed in hardware. */
/* 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/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
index f4f30d0c25c4..67c5d4eb32ac 100644
--- a/arch/x86/kvm/cpuid.c
+++ b/arch/x86/kvm/cpuid.c
@@ -27,6 +27,12 @@
#include "trace.h"
#include "pmu.h"
+static bool __read_mostly expose_amd_ssb_no = 0;
+module_param(expose_amd_ssb_no, bool, S_IRUGO | S_IWUSR);
+
+static bool __read_mostly expose_amd_spec_ctrl = 0;
+module_param(expose_amd_spec_ctrl, bool, S_IRUGO | S_IWUSR);
+
static u32 xstate_required_size(u64 xstate_bv, bool compacted)
{
int feature_bit = 0;
@@ -672,6 +678,12 @@ static inline int __do_cpuid_ent(struct kvm_cpuid_entry2 *entry, u32 function,
if (boot_cpu_has(X86_FEATURE_LS_CFG_SSBD) &&
!boot_cpu_has(X86_FEATURE_AMD_SSBD))
entry->ebx |= F(VIRT_SSBD);
+
+ if (expose_amd_spec_ctrl && !boot_cpu_has(X86_FEATURE_HYPERVISOR))
+ entry->ebx |= F(AMD_SSBD);
+
+ if (expose_amd_ssb_no && !boot_cpu_has(X86_FEATURE_HYPERVISOR))
+ entry->ebx |= F(AMD_SSB_NO);
break;
}
case 0x80000019:
diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
index 950ec50f77c3..a4c71b37df74 100644
--- a/arch/x86/kvm/svm.c
+++ b/arch/x86/kvm/svm.c
@@ -288,7 +288,6 @@ static const struct svm_direct_access_msrs {
{ .index = MSR_CSTAR, .always = true },
{ .index = MSR_SYSCALL_MASK, .always = true },
#endif
- { .index = MSR_IA32_SPEC_CTRL, .always = false },
{ .index = MSR_IA32_PRED_CMD, .always = false },
{ .index = MSR_IA32_LASTBRANCHFROMIP, .always = false },
{ .index = MSR_IA32_LASTBRANCHTOIP, .always = false },
@@ -4231,18 +4230,6 @@ static int svm_set_msr(struct kvm_vcpu *vcpu, struct msr_data *msr)
if (!data)
break;
- /*
- * For non-nested:
- * When it's written (to non-zero) for the first time, pass
- * it through.
- *
- * For nested:
- * The handling of the MSR bitmap for L2 guests is done in
- * nested_svm_vmrun_msrpm.
- * We update the L1 MSR bit as well since it will end up
- * touching the MSR anyway now.
- */
- set_msr_interception(svm->msrpm, MSR_IA32_SPEC_CTRL, 1, 1);
break;
case MSR_IA32_PRED_CMD:
if (!msr->host_initiated &&
--
2.13.4
