From 54dacb5c02cba4676879ed077765734326b78e39 Mon Sep 17 00:00:00 2001 From: Andrew Cooper Date: Tue, 5 Mar 2024 12:01:22 +0100 Subject: [PATCH 36/67] x86/cpu-policy: Allow for levelling of VERW side effects MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit MD_CLEAR and FB_CLEAR need OR-ing across a migrate pool. Allow this, by having them unconditinally set in max, with the host values reflected in default. Annotate the bits as having special properies. Signed-off-by: Andrew Cooper Reviewed-by: Roger Pau Monné master commit: de17162cafd27f2865a3102a2ec0f386a02ed03d master date: 2024-03-01 20:14:19 +0000 --- xen/arch/x86/cpu-policy.c | 24 +++++++++++++++++++++ xen/arch/x86/include/asm/cpufeature.h | 1 + xen/include/public/arch-x86/cpufeatureset.h | 4 ++-- 3 files changed, 27 insertions(+), 2 deletions(-) diff --git a/xen/arch/x86/cpu-policy.c b/xen/arch/x86/cpu-policy.c index f0f2c8a1c0..7b875a7221 100644 --- a/xen/arch/x86/cpu-policy.c +++ b/xen/arch/x86/cpu-policy.c @@ -435,6 +435,16 @@ static void __init guest_common_max_feature_adjustments(uint32_t *fs) __set_bit(X86_FEATURE_RSBA, fs); __set_bit(X86_FEATURE_RRSBA, fs); + /* + * These bits indicate that the VERW instruction may have gained + * scrubbing side effects. With pooling, they mean "you might migrate + * somewhere where scrubbing is necessary", and may need exposing on + * unaffected hardware. This is fine, because the VERW instruction + * has been around since the 286. + */ + __set_bit(X86_FEATURE_MD_CLEAR, fs); + __set_bit(X86_FEATURE_FB_CLEAR, fs); + /* * The Gather Data Sampling microcode mitigation (August 2023) has an * adverse performance impact on the CLWB instruction on SKX/CLX/CPX. @@ -469,6 +479,20 @@ static void __init guest_common_default_feature_adjustments(uint32_t *fs) cpu_has_rdrand && !is_forced_cpu_cap(X86_FEATURE_RDRAND) ) __clear_bit(X86_FEATURE_RDRAND, fs); + /* + * These bits indicate that the VERW instruction may have gained + * scrubbing side effects. The max policy has them set for migration + * reasons, so reset the default policy back to the host values in + * case we're unaffected. + */ + __clear_bit(X86_FEATURE_MD_CLEAR, fs); + if ( cpu_has_md_clear ) + __set_bit(X86_FEATURE_MD_CLEAR, fs); + + __clear_bit(X86_FEATURE_FB_CLEAR, fs); + if ( cpu_has_fb_clear ) + __set_bit(X86_FEATURE_FB_CLEAR, fs); + /* * The Gather Data Sampling microcode mitigation (August 2023) has an * adverse performance impact on the CLWB instruction on SKX/CLX/CPX. diff --git a/xen/arch/x86/include/asm/cpufeature.h b/xen/arch/x86/include/asm/cpufeature.h index 9ef7756593..ec824e8954 100644 --- a/xen/arch/x86/include/asm/cpufeature.h +++ b/xen/arch/x86/include/asm/cpufeature.h @@ -136,6 +136,7 @@ #define cpu_has_avx512_4fmaps boot_cpu_has(X86_FEATURE_AVX512_4FMAPS) #define cpu_has_avx512_vp2intersect boot_cpu_has(X86_FEATURE_AVX512_VP2INTERSECT) #define cpu_has_srbds_ctrl boot_cpu_has(X86_FEATURE_SRBDS_CTRL) +#define cpu_has_md_clear boot_cpu_has(X86_FEATURE_MD_CLEAR) #define cpu_has_rtm_always_abort boot_cpu_has(X86_FEATURE_RTM_ALWAYS_ABORT) #define cpu_has_tsx_force_abort boot_cpu_has(X86_FEATURE_TSX_FORCE_ABORT) #define cpu_has_serialize boot_cpu_has(X86_FEATURE_SERIALIZE) diff --git a/xen/include/public/arch-x86/cpufeatureset.h b/xen/include/public/arch-x86/cpufeatureset.h index 94d211df2f..aec1407613 100644 --- a/xen/include/public/arch-x86/cpufeatureset.h +++ b/xen/include/public/arch-x86/cpufeatureset.h @@ -260,7 +260,7 @@ XEN_CPUFEATURE(AVX512_4FMAPS, 9*32+ 3) /*A AVX512 Multiply Accumulation Single XEN_CPUFEATURE(FSRM, 9*32+ 4) /*A Fast Short REP MOVS */ XEN_CPUFEATURE(AVX512_VP2INTERSECT, 9*32+8) /*a VP2INTERSECT{D,Q} insns */ XEN_CPUFEATURE(SRBDS_CTRL, 9*32+ 9) /* MSR_MCU_OPT_CTRL and RNGDS_MITG_DIS. */ -XEN_CPUFEATURE(MD_CLEAR, 9*32+10) /*A VERW clears microarchitectural buffers */ +XEN_CPUFEATURE(MD_CLEAR, 9*32+10) /*!A VERW clears microarchitectural buffers */ XEN_CPUFEATURE(RTM_ALWAYS_ABORT, 9*32+11) /*! June 2021 TSX defeaturing in microcode. */ XEN_CPUFEATURE(TSX_FORCE_ABORT, 9*32+13) /* MSR_TSX_FORCE_ABORT.RTM_ABORT */ XEN_CPUFEATURE(SERIALIZE, 9*32+14) /*A SERIALIZE insn */ @@ -321,7 +321,7 @@ XEN_CPUFEATURE(DOITM, 16*32+12) /* Data Operand Invariant Timing XEN_CPUFEATURE(SBDR_SSDP_NO, 16*32+13) /*A No Shared Buffer Data Read or Sideband Stale Data Propagation */ XEN_CPUFEATURE(FBSDP_NO, 16*32+14) /*A No Fill Buffer Stale Data Propagation */ XEN_CPUFEATURE(PSDP_NO, 16*32+15) /*A No Primary Stale Data Propagation */ -XEN_CPUFEATURE(FB_CLEAR, 16*32+17) /*A Fill Buffers cleared by VERW */ +XEN_CPUFEATURE(FB_CLEAR, 16*32+17) /*!A Fill Buffers cleared by VERW */ XEN_CPUFEATURE(FB_CLEAR_CTRL, 16*32+18) /* MSR_OPT_CPU_CTRL.FB_CLEAR_DIS */ XEN_CPUFEATURE(RRSBA, 16*32+19) /*! Restricted RSB Alternative */ XEN_CPUFEATURE(BHI_NO, 16*32+20) /*A No Branch History Injection */ -- 2.44.0