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Date: Mon, 4 Mar 2019 18:01:54 +0800
From: Yang Weijiang <weijiang.yang@...el.com>
To: Sean Christopherson <sean.j.christopherson@...el.com>
Cc: pbonzini@...hat.com, rkrcmar@...hat.com, jmattson@...gle.com,
linux-kernel@...r.kernel.org, kvm@...r.kernel.org, mst@...hat.com,
yu-cheng.yu@...el.com, Zhang Yi Z <yi.z.zhang@...ux.intel.com>
Subject: Re: [PATCH v3 3/8] KVM:CPUID: Add CPUID support for Guest CET
On Mon, Mar 04, 2019 at 10:47:53AM -0800, Sean Christopherson wrote:
> On Mon, Feb 25, 2019 at 09:27:11PM +0800, Yang Weijiang wrote:
> > Guest CET SHSTK and IBT capability are reported via
> > CPUID.(EAX=7, ECX=0):ECX[bit 7] and EDX[bit 20] respectively.
> > Guest user mode and supervisor mode xsaves component size
> > is reported via CPUID.(EAX=0xD, ECX=1):ECX[bit 11] and ECX[bit 12]
> > respectively.
> >
> > Signed-off-by: Zhang Yi Z <yi.z.zhang@...ux.intel.com>
> > Signed-off-by: Yang Weijiang <weijiang.yang@...el.com>
> > ---
> > arch/x86/kvm/cpuid.c | 60 +++++++++++++++++++++++++++++++++-----------
> > arch/x86/kvm/x86.h | 4 +++
> > 2 files changed, 50 insertions(+), 14 deletions(-)
> >
> > diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
> > index cb1aece25b17..5e05756cc6db 100644
> > --- a/arch/x86/kvm/cpuid.c
> > +++ b/arch/x86/kvm/cpuid.c
> > @@ -65,6 +65,16 @@ u64 kvm_supported_xcr0(void)
> > return xcr0;
> > }
> >
> > +u64 kvm_supported_xss(void)
> > +{
> > + u64 xss;
> > +
> > + rdmsrl(MSR_IA32_XSS, xss);
>
> Honest question as I haven't thought through the flows: do we actually
> need to restrict XSS based on what's enabled in the host? This
> conflicts with your other statements that CET features can be enabled
> independent of host support.
>
> And if we do incorporate the host status, the value should be read once
> and cached unless we're expecting the host value to change dynamically,
> e.g. see host_efer.
>
> > + xss &= KVM_SUPPORTED_XSS;
> > + return xss;
> > +}
> > +EXPORT_SYMBOL(kvm_supported_xss);
> > +
> > #define F(x) bit(X86_FEATURE_##x)
> >
> > /* For scattered features from cpufeatures.h; we currently expose none */
> > @@ -323,6 +333,7 @@ static inline int __do_cpuid_ent(struct kvm_cpuid_entry2 *entry, u32 function,
> > u32 index, int *nent, int maxnent)
> > {
> > int r;
> > + u32 eax, ebx, ecx, edx;
> > unsigned f_nx = is_efer_nx() ? F(NX) : 0;
> > #ifdef CONFIG_X86_64
> > unsigned f_gbpages = (kvm_x86_ops->get_lpage_level() == PT_PDPE_LEVEL)
> > @@ -503,6 +514,20 @@ static inline int __do_cpuid_ent(struct kvm_cpuid_entry2 *entry, u32 function,
> > * if the host doesn't support it.
> > */
> > entry->edx |= F(ARCH_CAPABILITIES);
> > +
> > + /*
> > + * Guest OS CET enabling is designed independent to
> > + * host enabling, it only has dependency on Host HW
> > + * capability, if it has, report CET support to
> > + * Guest.
> > + */
> > + cpuid_count(7, 0, &eax, &ebx, &ecx, &edx);
> > + if (ecx & F(SHSTK))
> > + entry->ecx |= F(SHSTK);
> > +
> > + if (edx & F(IBT))
> > + entry->edx |= F(IBT);
> > +
> > } else {
> > entry->ebx = 0;
> > entry->ecx = 0;
> > @@ -564,14 +589,17 @@ static inline int __do_cpuid_ent(struct kvm_cpuid_entry2 *entry, u32 function,
> > }
> > case 0xd: {
> > int idx, i;
> > - u64 supported = kvm_supported_xcr0();
> > + u64 u_supported = kvm_supported_xcr0();
> > + u64 s_supported = kvm_supported_xss();
> > + u64 supported;
> > + int compacted;
> >
> > - entry->eax &= supported;
> > - entry->ebx = xstate_required_size(supported, false);
> > + entry->eax &= u_supported;
> > + entry->ebx = xstate_required_size(u_supported, false);
> > entry->ecx = entry->ebx;
> > - entry->edx &= supported >> 32;
> > + entry->edx &= u_supported >> 32;
> > entry->flags |= KVM_CPUID_FLAG_SIGNIFCANT_INDEX;
> > - if (!supported)
> > + if (!u_supported && !s_supported)
> > break;
> >
> > for (idx = 1, i = 1; idx < 64; ++idx) {
> > @@ -583,19 +611,23 @@ static inline int __do_cpuid_ent(struct kvm_cpuid_entry2 *entry, u32 function,
> > if (idx == 1) {
> > entry[i].eax &= kvm_cpuid_D_1_eax_x86_features;
> > cpuid_mask(&entry[i].eax, CPUID_D_1_EAX);
> > - entry[i].ebx = 0;
> > - if (entry[i].eax & (F(XSAVES)|F(XSAVEC)))
> > - entry[i].ebx =
> > - xstate_required_size(supported,
> > - true);
> > + supported = u_supported | s_supported;
> > + compacted = entry[i].eax &
> > + (F(XSAVES) | F(XSAVEC));
> > + entry[i].ebx = xstate_required_size(supported,
> > + compacted);
> > + entry[i].ecx &= s_supported;
> > + entry[i].edx = 0;
> > } else {
> > + supported = (entry[i].ecx & 1) ? s_supported :
> > + u_supported;
> > if (entry[i].eax == 0 || !(supported & mask))
> > continue;
> > - if (WARN_ON_ONCE(entry[i].ecx & 1))
> > - continue;
> > + entry[i].ecx &= 1;
> > + entry[i].edx = 0;
> > + if (entry[i].ecx)
> > + entry[i].ebx = 0;
> > }
> > - entry[i].ecx = 0;
> > - entry[i].edx = 0;
> > entry[i].flags |=
> > KVM_CPUID_FLAG_SIGNIFCANT_INDEX;
> > ++*nent;
> > diff --git a/arch/x86/kvm/x86.h b/arch/x86/kvm/x86.h
> > index 224cd0a47568..c61da41c3c5c 100644
> > --- a/arch/x86/kvm/x86.h
> > +++ b/arch/x86/kvm/x86.h
> > @@ -283,6 +283,10 @@ int x86_emulate_instruction(struct kvm_vcpu *vcpu, unsigned long cr2,
> > | XFEATURE_MASK_YMM | XFEATURE_MASK_BNDREGS \
> > | XFEATURE_MASK_BNDCSR | XFEATURE_MASK_AVX512 \
> > | XFEATURE_MASK_PKRU)
> > +
> > +#define KVM_SUPPORTED_XSS (XFEATURE_MASK_SHSTK_USER \
> > + | XFEATURE_MASK_SHSTK_KERNEL)
>
> I don't think these definitions are correct, the spec I have lists them
> as CET_U and CET_S, i.e. they aren't specific to SHSTK. Did these names
> get inherited from the kernel enabling patches?
>
Yes, exactly, I'll notify kernel developer of the issue.
> > +
> > extern u64 host_xcr0;
> >
> > extern u64 kvm_supported_xcr0(void);
> > --
> > 2.17.1
> >
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