linux-kernel.vger.kernel.org archive mirror
 help / color / mirror / Atom feed
From: Sean Christopherson <sean.j.christopherson@intel.com>
To: Yang Weijiang <weijiang.yang@intel.com>
Cc: "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: Tue, 22 Oct 2019 13:13:21 -0700	[thread overview]
Message-ID: <20191022201321.GN2343@linux.intel.com> (raw)
In-Reply-To: <20191018015802.GD2286@local-michael-cet-test>

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.

  reply	other threads:[~2019-10-22 20:13 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 [this message]
2019-10-23  1:19           ` Yang Weijiang
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

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=20191022201321.GN2343@linux.intel.com \
    --to=sean.j.christopherson@intel.com \
    --cc=jmattson@google.com \
    --cc=kvm@vger.kernel.org \
    --cc=linux-kernel@vger.kernel.org \
    --cc=mst@redhat.com \
    --cc=pbonzini@redhat.com \
    --cc=rkrcmar@redhat.com \
    --cc=weijiang.yang@intel.com \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line before the message body. 
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).