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Re: [Xen-devel] [PATCH RFC] x86/resume: take care of fully eager FPU around system suspend
- To: Jan Beulich <jbeulich@xxxxxxxx>, <xen-devel@xxxxxxxxxxxxxxxxxxxx>
- From: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
- Date: Mon, 18 Jun 2018 16:45:39 +0800
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- Cc: Juergen Gross <jgross@xxxxxxxx>
- Delivery-date: Mon, 18 Jun 2018 08:45:55 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
- Openpgp: preference=signencrypt
On 17/06/18 16:56, Jan Beulich wrote:
> Just like in the HVM emulation and EFI runtime call cases we must not
> set CR0.TS here in fully eager mode. Note that idle vCPU-s never have
> ->arch.fully_eager_fpu set (for their initialization not going through
> vcpu_init_fpu()), so we won't hit the respective ASSERT() in
> vcpu_restore_fpu_eager().
>
> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
> ---
> RFC: Not even compile tested, as I'm writing this from home. Also please
> excuse the formatting (hence the attachment) - our mail web frontend
> doesn't allow anything better.
>
> --- a/xen/arch/x86/acpi/suspend.c
> +++ b/xen/arch/x86/acpi/suspend.c
> @@ -92,8 +92,11 @@ void restore_rest_processor_state(void)
> write_debugreg(7, curr->arch.debugreg[7]);
> }
>
> - /* Reload FPU state on next FPU use. */
> - stts();
> + /* Reload FPU state immediately or on next FPU use. */
> + if ( curr->arch.fully_eager_fpu )
> + vcpu_restore_fpu_eager(curr);
> + else
> + stts();
Hmm - thinking about it, this should either be nothing, or a straight
call to vcpu_restore_fpu_eager(curr).
If it is necessary here, then I cant see how the non-lazy xsave states
currently work.
OTOH, we could probably drop a large quantity of this custom
save/restore logic if we force a transition to full idle before taking
the S3 path, at which point the normal ctxt_switch_to() path should DTRT.
~Andrew
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