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

[Avi Kivity <avi@redhat.com>]

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@intel.com>
> ---
>  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.


-- 
error compiling committee.c: too many arguments to function