From: Xiao Guangrong <guangrong.xiao@linux.intel.com>
To: David Matlack <dmatlack@google.com>,
linux-kernel@vger.kernel.org, x86@kernel.org,
kvm@vger.kernel.org
Cc: pbonzini@redhat.com, mingo@redhat.com, luto@kernel.org,
hpa@zytor.com, digitaleric@google.com
Subject: Re: [PATCH 0/1] KVM: x86: using the fpu in interrupt context with a guest's xcr0
Date: Mon, 14 Mar 2016 15:46:31 +0800 [thread overview]
Message-ID: <56E66C57.9080802@linux.intel.com> (raw)
In-Reply-To: <1457729240-3846-1-git-send-email-dmatlack@google.com>
On 03/12/2016 04:47 AM, David Matlack wrote:
> I have not been able to trigger this bug on Linux 4.3, and suspect
> it is due to this commit from Linux 4.2:
>
> 653f52c kvm,x86: load guest FPU context more eagerly
>
> With this commit, as long as the host is using eagerfpu, the guest's
> fpu is always loaded just before the guest's xcr0 (vcpu->fpu_active
> is always 1 in the following snippet):
>
> 6569 if (vcpu->fpu_active)
> 6570 kvm_load_guest_fpu(vcpu);
> 6571 kvm_load_guest_xcr0(vcpu);
>
> When the guest's fpu is loaded, irq_fpu_usable() returns false.
Er, i did not see that commit introduced this change.
>
> We've included our workaround for this bug, which applies to Linux 3.11.
> It does not apply cleanly to HEAD since the fpu subsystem was refactored
> in Linux 4.2. While the latest kernel does not look vulnerable, we may
> want to apply a fix to the vulnerable stable kernels.
Is the latest kvm safe if we use !eager fpu? Under this case, kvm_load_guest_fpu()
is not called for every single VM-enter, that means kernel will use guest's xcr0 to
save/restore XSAVE area.
Maybe a simpler fix is just calling __kernel_fpu_begin() when the CPU switches
to vCPU and reverts it when the vCPU is scheduled out or returns to userspace.
next prev parent reply other threads:[~2016-03-14 7:47 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-03-11 20:47 [PATCH 0/1] KVM: x86: using the fpu in interrupt context with a guest's xcr0 David Matlack
2016-03-11 20:47 ` [PATCH 1/1] KVM: don't allow irq_fpu_usable when the VCPU's XCR0 is loaded David Matlack
2016-03-11 21:14 ` Andy Lutomirski
2016-03-11 21:33 ` David Matlack
2016-03-14 13:17 ` Paolo Bonzini
2016-03-15 18:27 ` Andy Lutomirski
2016-03-15 19:32 ` Paolo Bonzini
2016-03-16 3:55 ` Xiao Guangrong
2016-03-16 12:01 ` Paolo Bonzini
2016-03-14 7:46 ` Xiao Guangrong [this message]
2016-03-15 19:01 ` [PATCH 0/1] KVM: x86: using the fpu in interrupt context with a guest's xcr0 David Matlack
2016-03-16 3:43 ` Xiao Guangrong
2016-03-16 3:48 ` Andy Lutomirski
2016-03-16 17:11 ` David Matlack
2016-03-16 17:09 ` David Matlack
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=56E66C57.9080802@linux.intel.com \
--to=guangrong.xiao@linux.intel.com \
--cc=digitaleric@google.com \
--cc=dmatlack@google.com \
--cc=hpa@zytor.com \
--cc=kvm@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=luto@kernel.org \
--cc=mingo@redhat.com \
--cc=pbonzini@redhat.com \
--cc=x86@kernel.org \
/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).