On 6/1/2018 9:59 AM, Konrad Rzeszutek Wilk wrote: Hi Konrad, Thanks for doing this. It was on my to-do list to get this support out after everything settled down. Just some questions/comments below. > The AMD document outlining the SSBD handling > 124441_AMD64_SpeculativeStoreBypassDisable_Whitepaper_final.pdf > mentions that if CPUID 8000_0008.EBX[24] is set we should be using > the SPEC_CTRL MSR (0x48) over the VIRT SPEC_CTRL MSR (0xC001_011f) > for speculative store bypass disable. > > This in effect means we should clear the X86_FEATURE_VIRT_SSBD > flag so that we would prefer the SPEC_CTRL MSR. > > See the document titled: > 124441_AMD64_SpeculativeStoreBypassDisable_Whitepaper_final.pdf > > A copy of this document is available at > https://bugzilla.kernel.org/show_bug.cgi?id=199889 > > Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx> > > --- > Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx> > Cc: Ingo Molnar <mingo@xxxxxxxxxx> > Cc: "H. Peter Anvin" <hpa@xxxxxxxxx> > Cc: Paolo Bonzini <pbonzini@xxxxxxxxxx> > Cc: "Radim Krčmář" <rkrcmar@xxxxxxxxxx> > Cc: Joerg Roedel <joro@xxxxxxxxxx> > Cc: Borislav Petkov <bp@xxxxxxx> > Cc: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx> > Cc: David Woodhouse <dwmw@xxxxxxxxxxxx> > Cc: Tom Lendacky <thomas.lendacky@xxxxxxx> > Cc: Janakarajan Natarajan <Janakarajan.Natarajan@xxxxxxx> > Cc: Kees Cook <keescook@xxxxxxxxxxxx> > Cc: KarimAllah Ahmed <karahmed@xxxxxxxxx> > Cc: Andy Lutomirski <luto@xxxxxxxxxx> > --- > arch/x86/include/asm/cpufeatures.h | 1 + > arch/x86/kernel/cpu/bugs.c | 12 +++++++----- > arch/x86/kernel/cpu/common.c | 6 ++++++ > arch/x86/kvm/cpuid.c | 10 ++++++++-- > arch/x86/kvm/svm.c | 8 +++++--- > 5 files changed, 27 insertions(+), 10 deletions(-) > > diff --git a/arch/x86/include/asm/cpufeatures.h b/arch/x86/include/asm/cpufeatures.h > index b6d7ce32927a..5701f5cecd31 100644 > --- 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_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. */ > > diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c > index 7416fc206b4a..6bea81855cdd 100644 > --- a/arch/x86/kernel/cpu/bugs.c > +++ b/arch/x86/kernel/cpu/bugs.c > @@ -529,18 +529,20 @@ static enum ssb_mitigation __init __ssb_select_mitigation(void) > if (mode == SPEC_STORE_BYPASS_DISABLE) { > setup_force_cpu_cap(X86_FEATURE_SPEC_STORE_BYPASS_DISABLE); > /* > - * Intel uses the SPEC CTRL MSR Bit(2) for this, while AMD uses > - * a completely different MSR and bit dependent on family. > + * Intel uses the SPEC CTRL MSR Bit(2) for this, while AMD may > + * use a completely different MSR and bit dependent on family. > */ > switch (boot_cpu_data.x86_vendor) { > case X86_VENDOR_INTEL: > + case X86_VENDOR_AMD: > + if (!static_cpu_has(X86_FEATURE_MSR_SPEC_CTRL)) { > + x86_amd_ssb_disable(); > + break; > + } > x86_spec_ctrl_base |= SPEC_CTRL_SSBD; > x86_spec_ctrl_mask |= SPEC_CTRL_SSBD; > wrmsrl(MSR_IA32_SPEC_CTRL, x86_spec_ctrl_base); > break; > - case X86_VENDOR_AMD: > - x86_amd_ssb_disable(); > - break; > } > } > > diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c > index 494735cf63f5..d08a29bd0385 100644 > --- a/arch/x86/kernel/cpu/common.c > +++ b/arch/x86/kernel/cpu/common.c > @@ -783,6 +783,12 @@ static void init_speculation_control(struct cpuinfo_x86 *c) > set_cpu_cap(c, X86_FEATURE_STIBP); > set_cpu_cap(c, X86_FEATURE_MSR_SPEC_CTRL); > } > + > + if (cpu_has(c, X86_FEATURE_AMD_SSBD)) { > + set_cpu_cap(c, X86_FEATURE_SSBD); > + set_cpu_cap(c, X86_FEATURE_MSR_SPEC_CTRL); > + clear_cpu_cap(c, X86_FEATURE_VIRT_SSBD); > + } > } > > void get_cpu_cap(struct cpuinfo_x86 *c) > diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c > index 132f8a58692e..f4f30d0c25c4 100644 > --- a/arch/x86/kvm/cpuid.c > +++ b/arch/x86/kvm/cpuid.c > @@ -379,7 +379,8 @@ static inline int __do_cpuid_ent(struct kvm_cpuid_entry2 *entry, u32 function, > > /* cpuid 0x80000008.ebx */ > const u32 kvm_cpuid_8000_0008_ebx_x86_features = > - F(AMD_IBPB) | F(AMD_IBRS) | F(VIRT_SSBD) | F(AMD_SSB_NO); > + F(AMD_IBPB) | F(AMD_IBRS) | F(AMD_SSBD) | F(VIRT_SSBD) | > + F(AMD_SSB_NO); > > /* cpuid 0xC0000001.edx */ > const u32 kvm_cpuid_C000_0001_edx_x86_features = > @@ -664,7 +665,12 @@ static inline int __do_cpuid_ent(struct kvm_cpuid_entry2 *entry, u32 function, > entry->ebx |= F(VIRT_SSBD); > entry->ebx &= kvm_cpuid_8000_0008_ebx_x86_features; > cpuid_mask(&entry->ebx, CPUID_8000_0008_EBX); > - if (boot_cpu_has(X86_FEATURE_LS_CFG_SSBD)) > + /* > + * The preference is to use SPEC CTRL MSR instead of the > + * VIRT_SPEC MSR. > + */ > + if (boot_cpu_has(X86_FEATURE_LS_CFG_SSBD) && > + !boot_cpu_has(X86_FEATURE_AMD_SSBD)) > entry->ebx |= F(VIRT_SSBD); > break; > } > diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c > index 26110c202b19..950ec50f77c3 100644 > --- a/arch/x86/kvm/svm.c > +++ b/arch/x86/kvm/svm.c > @@ -4115,7 +4115,8 @@ static int svm_get_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info) > break; > case MSR_IA32_SPEC_CTRL: > if (!msr_info->host_initiated && > - !guest_cpuid_has(vcpu, X86_FEATURE_AMD_IBRS)) > + !guest_cpuid_has(vcpu, X86_FEATURE_AMD_IBRS) && > + !guest_cpuid_has(vcpu, X86_FEATURE_AMD_SSBD)) Shouldn't the IBRS/SSBD check be an "or" check? I don't think it's necessarily true that IBRS and SSBD have to both be set. Maybe something like: if (!msr_info->host_initiated && !(guest_cpuid_has(vcpu, X86_FEATURE_AMD_IBRS) || guest_cpuid_has(vcpu, X86_FEATURE_AMD_SSBD)) Does that make sense? > return 1; > > msr_info->data = svm->spec_ctrl; > @@ -4217,11 +4218,12 @@ static int svm_set_msr(struct kvm_vcpu *vcpu, struct msr_data *msr) > break; > case MSR_IA32_SPEC_CTRL: > if (!msr->host_initiated && > - !guest_cpuid_has(vcpu, X86_FEATURE_AMD_IBRS)) > + !guest_cpuid_has(vcpu, X86_FEATURE_AMD_IBRS) && > + !guest_cpuid_has(vcpu, X86_FEATURE_AMD_SSBD)) Same question as above. Thanks, Tom > return 1; > > /* The STIBP bit doesn't fault even if it's not advertised */ > - if (data & ~(SPEC_CTRL_IBRS | SPEC_CTRL_STIBP)) > + if (data & ~(SPEC_CTRL_IBRS | SPEC_CTRL_STIBP | SPEC_CTRL_SSBD)) > return 1; > > svm->spec_ctrl = data; >
