From: Yang Weijiang <weijiang.yang@intel.com>
To: Sean Christopherson <sean.j.christopherson@intel.com>
Cc: "Yang Weijiang" <weijiang.yang@intel.com>,
"Jim Mattson" <jmattson@google.com>,
"kvm list" <kvm@vger.kernel.org>,
LKML <linux-kernel@vger.kernel.org>,
"Paolo Bonzini" <pbonzini@redhat.com>,
"Michael S. Tsirkin" <mst@redhat.com>,
"Radim Krčmář" <rkrcmar@redhat.com>
Subject: Re: [PATCH v7 5/7] kvm: x86: Add CET CR4 bit and XSS support
Date: Wed, 23 Oct 2019 09:19:51 +0800 [thread overview]
Message-ID: <20191023011951.GB27009@local-michael-cet-test> (raw)
In-Reply-To: <20191022201321.GN2343@linux.intel.com>
On Tue, Oct 22, 2019 at 01:13:21PM -0700, Sean Christopherson wrote:
> On Fri, Oct 18, 2019 at 09:58:02AM +0800, Yang Weijiang wrote:
> > On Thu, Oct 17, 2019 at 12:56:42PM -0700, Sean Christopherson wrote:
> > > On Wed, Oct 02, 2019 at 12:05:23PM -0700, Jim Mattson wrote:
> > > > > + u64 kvm_xss = kvm_supported_xss();
> > > > > +
> > > > > + best->ebx =
> > > > > + xstate_required_size(vcpu->arch.xcr0 | kvm_xss, true);
> > > >
> > > > Shouldn't this size be based on the *current* IA32_XSS value, rather
> > > > than the supported IA32_XSS bits? (i.e.
> > > > s/kvm_xss/vcpu->arch.ia32_xss/)
> > >
> > > Ya.
> > >
> > I'm not sure if I understand correctly, kvm_xss is what KVM supports,
> > but arch.ia32_xss reflects what guest currently is using, shoudn't CPUID
> > report what KVM supports instead of current status?
> > Will CPUID match current IA32_XSS status if guest changes it runtime?
>
> Not in this case. Select CPUID output is dependent on current state as
> opposed to being a constant defind by hardware. Per the SDM, EBX is:
>
> The size in bytes of the XSAVE area containing all states enabled by
> XCRO | IA32_XSS
>
> Since KVM is emulating CPUID for the guest, XCR0 and IA32_XSS in this
> context refers to the guest's current/actual XCR0/IA32_XSS values. The
> purpose of this behavior is so that software can call CPUID to query the
> actual amount of memory that is needed for XSAVE(S), as opposed to the
> absolute max size that _might_ be needed.
>
> MONITOR/MWAIT is the other case that comes to mind where CPUID dynamically
> reflects configured state, e.g. MWAIT is reported as unsupported if it's
> disabled via IA32_MISC_ENABLE MSR.
Yep, make sense, thank you for explanation.
next prev parent reply other threads:[~2019-10-23 1:17 UTC|newest]
Thread overview: 43+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-09-27 2:19 [PATCH v7 0/7] Introduce support for Guest CET feature Yang Weijiang
2019-09-27 2:19 ` [PATCH v7 1/7] KVM: CPUID: Fix IA32_XSS support in CPUID(0xd,i) enumeration Yang Weijiang
2019-10-02 17:26 ` Jim Mattson
2019-10-08 8:30 ` Yang Weijiang
2019-10-17 19:46 ` Sean Christopherson
2019-10-18 1:28 ` Yang Weijiang
2019-10-22 19:46 ` Sean Christopherson
2019-10-23 1:16 ` Yang Weijiang
2019-09-27 2:19 ` [PATCH v7 2/7] kvm: vmx: Define CET VMCS fields and CPUID flags Yang Weijiang
2019-10-02 18:04 ` Jim Mattson
2019-10-09 5:56 ` Yang Weijiang
2019-09-27 2:19 ` [PATCH v7 3/7] KVM: VMX: Pass through CET related MSRs to Guest Yang Weijiang
2019-10-02 18:18 ` Jim Mattson
2019-10-09 6:15 ` Yang Weijiang
2019-10-10 19:04 ` Jim Mattson
2019-10-11 1:51 ` Yang Weijiang
2019-10-17 20:04 ` Sean Christopherson
2019-10-18 1:31 ` Yang Weijiang
2019-09-27 2:19 ` [PATCH v7 4/7] KVM: VMX: Load Guest CET via VMCS when CET is enabled in Guest Yang Weijiang
2019-10-02 18:54 ` Jim Mattson
2019-10-09 6:43 ` Yang Weijiang
2019-10-09 23:08 ` Jim Mattson
2019-10-10 1:30 ` Yang Weijiang
2019-10-10 23:44 ` Jim Mattson
2019-10-11 1:43 ` Yang Weijiang
2019-09-27 2:19 ` [PATCH v7 5/7] kvm: x86: Add CET CR4 bit and XSS support Yang Weijiang
2019-10-02 19:05 ` Jim Mattson
2019-10-17 19:56 ` Sean Christopherson
2019-10-18 1:58 ` Yang Weijiang
2019-10-22 20:13 ` Sean Christopherson
2019-10-23 1:19 ` Yang Weijiang [this message]
2019-09-27 2:19 ` [PATCH v7 6/7] KVM: x86: Load Guest fpu state when accessing MSRs managed by XSAVES Yang Weijiang
2019-10-02 19:56 ` Jim Mattson
2019-10-09 6:46 ` Yang Weijiang
2019-09-27 2:19 ` [PATCH v7 7/7] KVM: x86: Add user-space access interface for CET MSRs Yang Weijiang
2019-10-02 20:57 ` Jim Mattson
2019-10-09 6:56 ` Yang Weijiang
2019-10-17 19:58 ` Sean Christopherson
2019-10-18 1:32 ` Yang Weijiang
2019-10-02 22:40 ` [PATCH v7 0/7] Introduce support for Guest CET feature Jim Mattson
2019-10-03 13:01 ` Yang Weijiang
2019-10-03 16:33 ` Jim Mattson
2019-10-08 8:50 ` Yang Weijiang
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