回复: 回复: [PATCH] target/i386: Clear xsave pkru bit when KVM XCR0 not support

[Yuchen <yu.chen@h3c.com>]

Paolo, thanks, 
The kernel patch can solve this problem. But it is difficult to upgrade the kernel in some production environments, 
and upgrading qemu is easy. This patch is just to sync qemu with kvm XSAVE features, no negative impact. 
At the same time, it increases the compatibility of qemu to kernel and improves the robustness of qemu.

> -----邮件原件-----
> 发件人: Paolo Bonzini <pbonzini@redhat.com>
> 发送时间: 2023年5月20日 1:37
> 收件人: yuchen (Cloud) <yu.chen@h3c.com>
> 主题: Re: 回复: [PATCH] target/i386: Clear xsave pkru bit when KVM
> XCR0 not support
> 
> On 5/18/23 14:37, Yuchen wrote:
> > Yes, because x86_cpu_xsave_all_areas() can get the correct XSAVE
> features.
> 
> If you tested it, I can post the patch as a workaround.  However, the
> kernel bug has been fixed too.
> 
> Paolo
> 
> >> -----邮件原件-----
> >> 发件人: Paolo Bonzini <pbonzini@redhat.com>
> >> 发送时间: 2023年5月18日 1:08
> >> 收件人: yuchen (Cloud) <yu.chen@h3c.com>;
> qemu-devel@nongnu.org
> >> 抄送: rth@twiddle.net; ehabkost@redhat.com; chengchiwen (Cloud)
> >> <chengchiwen@h3c.com>
> >> 主题: Re: [PATCH] target/i386: Clear xsave pkru bit when KVM XCR0
> not
> >> support
> >>
> >> On 5/17/23 12:55, Yuchen wrote:
> >>> Migrating guest from Intel new CPU (as Gold 6230) to old CPU (as
> >>> E5-2650 v4) will pause on the destination host. Because old CPU not
> >>> support xsave pkru feature, and KVM KVM_SET_XSAVE ioctl return
> >> EINVAL.
> >>>
> >>> This kernel commit introduces the problem:
> >>>
> >>> ea4d6938d4c0 x86/fpu: Replace KVMs home brewed FPU copy from
> >> user
> >>>
> >>> Signed-off-by: YuChen <yu.chen@h3c.com>
> >>
> >> Would this work instead?
> >>
> >> diff --git a/target/i386/xsave_helper.c b/target/i386/xsave_helper.c
> >> index 996e9f3bfef5..d3e5edad2ecd 100644
> >> --- a/target/i386/xsave_helper.c
> >> +++ b/target/i386/xsave_helper.c
> >> @@ -47,7 +47,7 @@ void x86_cpu_xsave_all_areas(X86CPU *cpu,
> void
> >> *buf, uint32_t buflen)
> >>            stq_p(xmm + 8, env->xmm_regs[i].ZMM_Q(1));
> >>        }
> >>
> >> -    header->xstate_bv = env->xstate_bv;
> >> +    header->xstate_bv = env->xstate_bv &
> >> + x86_cpu_xsave_xcr0_components(cpu);
> >>
> >>        e = &x86_ext_save_areas[XSTATE_YMM_BIT];
> >>        if (e->size && e->offset) {
> >>
> >> Paolo
> >
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