From: Paolo Bonzini <pbonzini@redhat.com>
To: Jim Mattson <jmattson@google.com>
Cc: Aaron Lewis <aaronlewis@google.com>,
Babu Moger <Babu.Moger@amd.com>,
Yang Weijiang <weijiang.yang@intel.com>,
Sebastian Andrzej Siewior <bigeasy@linutronix.de>,
kvm list <kvm@vger.kernel.org>, Luwei Kang <luwei.kang@intel.com>
Subject: Re: [Patch 3/6] kvm: svm: Add support for XSAVES on AMD
Date: Wed, 9 Oct 2019 23:40:52 +0200 [thread overview]
Message-ID: <9335c3c7-e2dd-cb2d-454a-c41143c94b63@redhat.com> (raw)
In-Reply-To: <CALMp9eRNdLdb7zR=wwx2tTc8n-ewCKuhrw9pxXGVQVUBjNpRow@mail.gmail.com>
On 09/10/19 23:29, Jim Mattson wrote:
> On Wed, Oct 9, 2019 at 12:02 AM Paolo Bonzini <pbonzini@redhat.com> wrote:
>>
>> On 09/10/19 02:41, Aaron Lewis wrote:
>>> - /*
>>> - * The only supported bit as of Skylake is bit 8, but
>>> - * it is not supported on KVM.
>>> - */
>>> - if (data != 0)
>>> - return 1;
>>
>> This comment is actually not true anymore; Intel supports PT (bit 8) on
>> Cascade Lake, so it could be changed to something like
>>
>> /*
>> * We do support PT (bit 8) if kvm_x86_ops->pt_supported(), but
>> * guests will have to configure it using WRMSR rather than
>> * XSAVES.
>> */
>>
>> Paolo
>
> Isn't it necessary for the host to set IA32_XSS to a superset of the
> guest IA32_XSS for proper host-level context-switching?
Yes, this is why we cannot allow the guest to set bit 8. But the
comment is obsolete:
1) of course Skylake is not the newest model
2) processor tracing was not supported at all when the comment was
written; but on CascadeLake, guest PT is now supported---just not the
processor tracing XSAVES component.
Paolo
> arch/x86/kernel/fpu/xstate.c has this comment:
>
> * Note that we do not currently set any bits on IA32_XSS so
> * 'XCR0 | IA32_XSS == XCR0' for now.
>
next prev parent reply other threads:[~2019-10-09 21:41 UTC|newest]
Thread overview: 25+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-10-09 0:41 [Patch 1/6] KVM: VMX: Remove unneeded check for X86_FEATURE_XSAVE Aaron Lewis
2019-10-09 0:41 ` [Patch 2/6] KVM: VMX: Use wrmsr for switching between guest and host IA32_XSS Aaron Lewis
2019-10-09 4:49 ` Yang Weijiang
2019-10-09 6:30 ` Paolo Bonzini
2019-10-09 12:34 ` Vitaly Kuznetsov
2019-10-09 6:31 ` Sebastian Andrzej Siewior
2019-10-09 0:41 ` [Patch 3/6] kvm: svm: Add support for XSAVES on AMD Aaron Lewis
2019-10-09 6:44 ` Sebastian Andrzej Siewior
2019-10-10 14:42 ` Aaron Lewis
2019-10-10 16:04 ` Paolo Bonzini
2019-10-09 7:01 ` Paolo Bonzini
2019-10-09 21:29 ` Jim Mattson
2019-10-09 21:40 ` Paolo Bonzini [this message]
2019-10-09 21:58 ` Jim Mattson
2019-10-09 22:49 ` Paolo Bonzini
2019-10-10 0:42 ` Kang, Luwei
2019-10-09 0:41 ` [Patch 4/6] kvm: svm: Enumerate XSAVES in guest CPUID when it is available to the guest Aaron Lewis
2019-10-09 1:42 ` Yang Weijiang
2019-10-09 6:32 ` Paolo Bonzini
2019-10-09 23:35 ` Jim Mattson
2019-10-09 0:41 ` [Patch 5/6] kvm: x86: Add IA32_XSS to the emulated_msrs list Aaron Lewis
2019-10-09 0:41 ` [Patch 6/6] kvm: tests: Add test to verify MSR_IA32_XSS Aaron Lewis
2019-10-09 6:30 ` Paolo Bonzini
2019-10-09 23:44 ` Jim Mattson
2019-10-10 16:01 ` Paolo Bonzini
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