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Message-ID: <fa831d0c-3e7b-b5ab-17a0-5d3b1bfd6142@amd.com>
Date: Fri, 1 Jun 2018 20:04:18 -0500
From: Tom Lendacky <thomas.lendacky@....com>
To: Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
linux-kernel@...r.kernel.org, kvm@...r.kernel.org, x86@...nel.org,
tglx@...utronix.de, andrew.cooper3@...rix.com
Cc: Ingo Molnar <mingo@...hat.com>, "H. Peter Anvin" <hpa@...or.com>,
Paolo Bonzini <pbonzini@...hat.com>,
Radim Krčmář <rkrcmar@...hat.com>,
Joerg Roedel <joro@...tes.org>, Borislav Petkov <bp@...e.de>,
David Woodhouse <dwmw@...zon.co.uk>,
Janakarajan Natarajan <Janakarajan.Natarajan@....com>,
Kees Cook <keescook@...omium.org>,
KarimAllah Ahmed <karahmed@...zon.de>,
Andy Lutomirski <luto@...nel.org>
Subject: Re: [PATCH v1 2/3] x86/bugs: Add AMD's SPEC_CTRL MSR usage
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@...cle.com>
>
> ---
> Cc: Thomas Gleixner <tglx@...utronix.de>
> Cc: Ingo Molnar <mingo@...hat.com>
> Cc: "H. Peter Anvin" <hpa@...or.com>
> Cc: Paolo Bonzini <pbonzini@...hat.com>
> Cc: "Radim Krčmář" <rkrcmar@...hat.com>
> Cc: Joerg Roedel <joro@...tes.org>
> Cc: Borislav Petkov <bp@...e.de>
> Cc: Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
> Cc: David Woodhouse <dwmw@...zon.co.uk>
> Cc: Tom Lendacky <thomas.lendacky@....com>
> Cc: Janakarajan Natarajan <Janakarajan.Natarajan@....com>
> Cc: Kees Cook <keescook@...omium.org>
> Cc: KarimAllah Ahmed <karahmed@...zon.de>
> Cc: Andy Lutomirski <luto@...nel.org>
> ---
> 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;
>
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