RE: [PATCH v2] kvm/fpu: Enable fully eager restore kvm FPU

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

 



> -----Original Message-----
> From: Avi Kivity [mailto:avi@xxxxxxxxxx]
> Sent: Wednesday, September 05, 2012 9:13 PM
> To: Hao, Xudong
> Cc: kvm@xxxxxxxxxxxxxxx; Zhang, Xiantao; Joerg.Roedel@xxxxxxx
> Subject: Re: [PATCH v2] kvm/fpu: Enable fully eager restore kvm FPU
> 
> On 09/05/2012 04:26 AM, Xudong Hao wrote:
> > Enable KVM FPU fully eager restore, if there is other FPU state which isn't
> > tracked by CR0.TS bit.
> >
> > Changes from v1:
> > Expand KVM_XSTATE_LAZY to 64 bits before negating it.
> >
> > Signed-off-by: Xudong Hao <xudong.hao@xxxxxxxxx>
> > ---
> >  arch/x86/include/asm/kvm.h |    4 ++++
> >  arch/x86/kvm/x86.c         |   13 ++++++++++++-
> >  2 files changed, 16 insertions(+), 1 deletions(-)
> >
> > diff --git a/arch/x86/include/asm/kvm.h b/arch/x86/include/asm/kvm.h
> > index 521bf25..4c27056 100644
> > --- a/arch/x86/include/asm/kvm.h
> > +++ b/arch/x86/include/asm/kvm.h
> > @@ -8,6 +8,8 @@
> >
> >  #include <linux/types.h>
> >  #include <linux/ioctl.h>
> > +#include <asm/user.h>
> > +#include <asm/xsave.h>
> >
> >  /* Select x86 specific features in <linux/kvm.h> */
> >  #define __KVM_HAVE_PIT
> > @@ -30,6 +32,8 @@
> >  /* Architectural interrupt line count. */
> >  #define KVM_NR_INTERRUPTS 256
> >
> > +#define KVM_XSTATE_LAZY	(XSTATE_FP | XSTATE_SSE | XSTATE_YMM)
> > +
> >  struct kvm_memory_alias {
> >  	__u32 slot;  /* this has a different namespace than memory slots */
> >  	__u32 flags;
> > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> > index 20f2266..a632042 100644
> > --- a/arch/x86/kvm/x86.c
> > +++ b/arch/x86/kvm/x86.c
> > @@ -5969,7 +5969,18 @@ void kvm_put_guest_fpu(struct kvm_vcpu *vcpu)
> >  	vcpu->guest_fpu_loaded = 0;
> >  	fpu_save_init(&vcpu->arch.guest_fpu);
> >  	++vcpu->stat.fpu_reload;
> > -	kvm_make_request(KVM_REQ_DEACTIVATE_FPU, vcpu);
> > +	/*
> > +	 * Currently KVM trigger FPU restore by #NM (via CR0.TS),
> > +	 * till now only XCR0.bit0, XCR0.bit1, XCR0.bit2 is tracked
> > +	 * by TS bit, there might be other FPU state is not tracked
> > +	 * by TS bit. Here it only make FPU deactivate request and do
> > +	 * FPU lazy restore for these cases: 1)xsave isn't enabled
> > +	 * in guest, 2)all guest FPU states can be tracked by TS bit.
> > +	 * For others, doing fully FPU eager restore.
> > +	 */
> > +	if (!kvm_read_cr4_bits(vcpu, X86_CR4_OSXSAVE) ||
> > +		!(vcpu->arch.xcr0 & ~((u64)KVM_XSTATE_LAZY)))
> > +		kvm_make_request(KVM_REQ_DEACTIVATE_FPU, vcpu);
> >  	trace_kvm_fpu(0);
> >  }
> >
> 
> I think something is missing.  This patch prevents
> KVM_REQ_DEACTIVATE_FPU, but the fpu may not be active when non-lazy bits
> are added to xcr0 (or cr4.osxsave is enabled).  I think you need to
> activate the fpu at that time as well.
> 

Mmh, I thought fpu is active by default, but it's better to make fpu active explicitly here.
If the following patch is fine, I'll make it another version.

-   kvm_make_request(KVM_REQ_DEACTIVATE_FPU, vcpu);
+   if (kvm_read_cr4_bits(vcpu, X86_CR4_OSXSAVE) &&
+       (vcpu->arch.xcr0 & ~((u64)KVM_XSTATE_LAZY)))
+       kvm_x86_ops->fpu_activate(vcpu);
+   else
+       kvm_make_request(KVM_REQ_DEACTIVATE_FPU, vcpu);


Thanks,
-Xudong


--
To unsubscribe from this list: send the line "unsubscribe kvm" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html


[Index of Archives]     [KVM ARM]     [KVM ia64]     [KVM ppc]     [Virtualization Tools]     [Spice Development]     [Libvirt]     [Libvirt Users]     [Linux USB Devel]     [Linux Audio Users]     [Yosemite Questions]     [Linux Kernel]     [Linux SCSI]     [XFree86]
  Powered by Linux