From: "Liu, Jing2" <jing2.liu@linux.intel.com>
To: Sean Christopherson <seanjc@google.com>
Cc: pbonzini@redhat.com, Vitaly Kuznetsov <vkuznets@redhat.com>,
Wanpeng Li <wanpengli@tencent.com>,
Jim Mattson <jmattson@google.com>, Joerg Roedel <joro@8bytes.org>,
Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
x86@kernel.org, "H. Peter Anvin" <hpa@zytor.com>,
kvm@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2] KVM: x86: Revise guest_fpu xcomp_bv field
Date: Tue, 9 Mar 2021 13:31:52 +0800 [thread overview]
Message-ID: <ffb71039-c77d-93d0-1e41-9f29d87d4532@linux.intel.com> (raw)
In-Reply-To: <YD1//+O57mr2D2Ne@google.com>
On 3/2/2021 7:59 AM, Sean Christopherson wrote:
> On Thu, Feb 25, 2021, Jing Liu wrote:
>> XCOMP_BV[63] field indicates that the save area is in the compacted
>> format and XCOMP_BV[62:0] indicates the states that have space allocated
>> in the save area, including both XCR0 and XSS bits enabled by the host
>> kernel. Use xfeatures_mask_all for calculating xcomp_bv and reuse
>> XCOMP_BV_COMPACTED_FORMAT defined by kernel.
>>
>> Signed-off-by: Jing Liu <jing2.liu@linux.intel.com>
>> ---
>> arch/x86/kvm/x86.c | 8 ++------
>> 1 file changed, 2 insertions(+), 6 deletions(-)
>>
>> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
>> index 1b404e4d7dd8..f115493f577d 100644
>> --- a/arch/x86/kvm/x86.c
>> +++ b/arch/x86/kvm/x86.c
>> @@ -4435,8 +4435,6 @@ static int kvm_vcpu_ioctl_x86_set_debugregs(struct kvm_vcpu *vcpu,
>> return 0;
>> }
>>
>> -#define XSTATE_COMPACTION_ENABLED (1ULL << 63)
>> -
>> static void fill_xsave(u8 *dest, struct kvm_vcpu *vcpu)
>> {
>> struct xregs_state *xsave = &vcpu->arch.guest_fpu->state.xsave;
>> @@ -4494,7 +4492,8 @@ static void load_xsave(struct kvm_vcpu *vcpu, u8 *src)
>> /* Set XSTATE_BV and possibly XCOMP_BV. */
>> xsave->header.xfeatures = xstate_bv;
>> if (boot_cpu_has(X86_FEATURE_XSAVES))
>> - xsave->header.xcomp_bv = host_xcr0 | XSTATE_COMPACTION_ENABLED;
>> + xsave->header.xcomp_bv = XCOMP_BV_COMPACTED_FORMAT |
>> + xfeatures_mask_all;
> Doesn't fill_xsave also need to be updated? Not with xfeatures_mask_all, but
> to account for arch.ia32_xss? I believe it's a nop with the current code, since
> supported_xss is zero, but it should be fixed, no?
Yes. For the arch.ia32_xss, I noticed CET
(https://lkml.org/lkml/2020/7/15/1412)
has posted related change so I didn't touch xstate_bv for fill_xsave for
now.
Finally, fill_xsave() need e.g. arch.guest_supported_xss for xstate_bv,
for xcomp_bv, xfeatures_mask_all is ok.
>
>>
>> /*
>> * Copy each region from the non-compacted offset to the
>> @@ -9912,9 +9911,6 @@ static void fx_init(struct kvm_vcpu *vcpu)
>> return;
>>
>> fpstate_init(&vcpu->arch.guest_fpu->state);
>> - if (boot_cpu_has(X86_FEATURE_XSAVES))
>> - vcpu->arch.guest_fpu->state.xsave.header.xcomp_bv =
>> - host_xcr0 | XSTATE_COMPACTION_ENABLED;
> Ugh, this _really_ needs a comment in the changelog. It took me a while to
> realize fpstate_init() does exactly what the new fill_xave() is doing.
How about introducing that "fx_init()->fpstate_init() initializes xcomp_bv
of guest_fpu so no need to set again in later fill_xsave() and
load_xsave()"
in commit message?
>
> And isn't the code in load_xsave() redundant and can be removed?
Oh, yes. Keep fx_init() initializing xcomp_bv for guest_fpu is enough.
Let me remove it in load_xsave later.
And for fill_xsave(), I think no need to set xcomp_bv there.
> Any code that
> uses get_xsave_addr() would be have a dependency on load_xsave() if it's not
> redundant, and I can't see how that would work.
Sorry I didn't quite understand why get_xsave_addr() has dependency on
load_xsave(), do you mean the xstate_bv instead of xcomp_bv, that
load_xsave()
uses it to get the addr?
Thanks,
Jing
>
>>
>> /*
>> * Ensure guest xcr0 is valid for loading
>> --
>> 2.18.4
>>
prev parent reply other threads:[~2021-03-09 5:32 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-02-25 10:49 [PATCH v2] KVM: x86: Revise guest_fpu xcomp_bv field Jing Liu
2021-03-01 23:59 ` Sean Christopherson
2021-03-09 5:31 ` Liu, Jing2 [this message]
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