From: Dave Hansen <dave.hansen@intel.com>
To: Sean Christopherson <sean.j.christopherson@intel.com>,
Paolo Bonzini <pbonzini@redhat.com>
Cc: Vitaly Kuznetsov <vkuznets@redhat.com>,
Wanpeng Li <wanpengli@tencent.com>,
Jim Mattson <jmattson@google.com>, Joerg Roedel <joro@8bytes.org>,
kvm@vger.kernel.org, linux-kernel@vger.kernel.org,
Derek Yerger <derek@djy.llc>,
kernel@najdan.com, Thomas Lambertz <mail@thomaslambertz.de>,
Rik van Riel <riel@surriel.com>,
Sebastian Andrzej Siewior <bigeasy@linutronix.de>,
Borislav Petkov <bp@suse.de>,
Thomas Gleixner <tglx@linutronix.de>
Subject: Re: [PATCH 1/4] KVM: x86: Handle TIF_NEED_FPU_LOAD in kvm_{load,put}_guest_fpu()
Date: Fri, 17 Jan 2020 10:31:53 -0800 [thread overview]
Message-ID: <4d5dca91-8dbc-9ff3-b67a-2fa963da29cf@intel.com> (raw)
In-Reply-To: <20200117062628.6233-2-sean.j.christopherson@intel.com>
On 1/16/20 10:26 PM, Sean Christopherson wrote:
> Handle TIF_NEED_FPU_LOAD similar to how fpu__copy() handles the flag
> when duplicating FPU state to a new task struct. TIF_NEED_FPU_LOAD can
> be set any time control is transferred out of KVM, be it voluntarily,
> e.g. if I/O is triggered during a KVM call to get_user_pages, or
> involuntarily, e.g. if softirq runs after an IRQ occurs. Therefore,
> KVM must account for TIF_NEED_FPU_LOAD whenever it is (potentially)
> accessing CPU FPU state.
>
> Fixes: 5f409e20b7945 ("x86/fpu: Defer FPU state load until return to userspace")
> Cc: stable@vger.kernel.org
> Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
> ---
> arch/x86/kvm/x86.c | 27 ++++++++++++++++++++++++---
> 1 file changed, 24 insertions(+), 3 deletions(-)
>
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index cf917139de6b..0c7211491f98 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -8476,8 +8476,20 @@ static void kvm_load_guest_fpu(struct kvm_vcpu *vcpu)
> {
> fpregs_lock();
>
> - copy_fpregs_to_fpstate(vcpu->arch.user_fpu);
> - /* PKRU is separately restored in kvm_x86_ops->run. */
> + /*
> + * If userspace's FPU state is not resident in the CPU registers, just
> + * memcpy() from current, else save CPU state directly to user_fpu.
> + */
> + if (test_thread_flag(TIF_NEED_FPU_LOAD))
> + memcpy(&vcpu->arch.user_fpu->state, ¤t->thread.fpu.state,
> + fpu_kernel_xstate_size);
> + else
> + copy_fpregs_to_fpstate(vcpu->arch.user_fpu);
> +
> + /*
> + * Load guest's FPU state to the CPU registers. PKRU is separately
> + * loaded in kvm_x86_ops->run.
> + */
> __copy_kernel_to_fpregs(&vcpu->arch.guest_fpu->state,
> ~XFEATURE_MASK_PKRU);
Nit: it took me a minute to realize that there is both:
vcpu->arch.user_fpu
and
vcpu->arch.guest_fpu
It might help readability to have local variables for those, or at least
a comment to help differentiate the two.
> @@ -8492,7 +8504,16 @@ static void kvm_put_guest_fpu(struct kvm_vcpu *vcpu)
> {
> fpregs_lock();
>
> - copy_fpregs_to_fpstate(vcpu->arch.guest_fpu);
> + /*
> + * If guest's FPU state is not resident in the CPU registers, just
> + * memcpy() from current, else save CPU state directly to guest_fpu.
> + */
> + if (test_thread_flag(TIF_NEED_FPU_LOAD))
> + memcpy(&vcpu->arch.guest_fpu->state, ¤t->thread.fpu.state,
> + fpu_kernel_xstate_size);
> + else
> + copy_fpregs_to_fpstate(vcpu->arch.guest_fpu);
> +
> copy_kernel_to_fpregs(&vcpu->arch.user_fpu->state);
>
> fpregs_mark_activate();
This also makes me wonder if we want to have copy_fpregs_to_fpstate()
check for TIF_NEED_FPU_LOAD and complain if it's set.
next prev parent reply other threads:[~2020-01-17 18:32 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-01-17 6:26 [PATCH 0/4] KVM: x86: TIF_NEED_FPU_LOAD bug fixes Sean Christopherson
2020-01-17 6:26 ` [PATCH 1/4] KVM: x86: Handle TIF_NEED_FPU_LOAD in kvm_{load,put}_guest_fpu() Sean Christopherson
2020-01-17 18:31 ` Dave Hansen [this message]
2020-01-17 18:43 ` Sean Christopherson
2020-01-17 6:26 ` [PATCH 2/4] KVM: x86: Ensure guest's FPU state is loaded when accessing for emulation Sean Christopherson
2020-01-17 6:26 ` [PATCH 3/4] KVM: x86: Revert "KVM: X86: Fix fpu state crash in kvm guest" Sean Christopherson
2020-03-04 7:41 ` Liu, Jing2
2020-03-04 7:58 ` Paolo Bonzini
2020-01-17 6:26 ` [PATCH 4/4] KVM: x86: Remove unused ctxt param from emulator's FPU accessors Sean Christopherson
2020-03-04 7:38 ` [PATCH 0/4] KVM: x86: TIF_NEED_FPU_LOAD bug fixes Liu, Jing2
2020-03-04 15:24 ` Sean Christopherson
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=4d5dca91-8dbc-9ff3-b67a-2fa963da29cf@intel.com \
--to=dave.hansen@intel.com \
--cc=bigeasy@linutronix.de \
--cc=bp@suse.de \
--cc=derek@djy.llc \
--cc=jmattson@google.com \
--cc=joro@8bytes.org \
--cc=kernel@najdan.com \
--cc=kvm@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=mail@thomaslambertz.de \
--cc=pbonzini@redhat.com \
--cc=riel@surriel.com \
--cc=sean.j.christopherson@intel.com \
--cc=tglx@linutronix.de \
--cc=vkuznets@redhat.com \
--cc=wanpengli@tencent.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).