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Re: [PATCH v1 3/8] x86/svm: Remove lazy FPU support
- To: Ross Lagerwall <ross.lagerwall@xxxxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxxx
- From: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
- Date: Thu, 19 Mar 2026 17:20:39 +0000
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- Cc: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, Jan Beulich <jbeulich@xxxxxxxx>, Roger Pau Monné <roger.pau@xxxxxxxxxx>, Jason Andryuk <jason.andryuk@xxxxxxx>
- Delivery-date: Thu, 19 Mar 2026 17:20:57 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 19/03/2026 1:29 pm, Ross Lagerwall wrote:
> Remove lazy FPU support from the SVM code since fully_eager_fpu is now
> always true.
>
> No functional change intended.
>
> Signed-off-by: Ross Lagerwall <ross.lagerwall@xxxxxxxxxx>
Reviewed-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
Unagling nestedsvm_fpu_vmentry() is tricky to follow but I've managed to
convince myself that it's correct.
> diff --git a/xen/arch/x86/hvm/svm/vmcb.c b/xen/arch/x86/hvm/svm/vmcb.c
> index e583ef8548c7..5ed7123d9a69 100644
> --- a/xen/arch/x86/hvm/svm/vmcb.c
> +++ b/xen/arch/x86/hvm/svm/vmcb.c
> @@ -138,9 +138,7 @@ static int construct_vmcb(struct vcpu *v)
>
> paging_update_paging_modes(v);
>
> - vmcb->_exception_intercepts =
> - HVM_TRAP_MASK |
> - (v->arch.fully_eager_fpu ? 0 : (1U << X86_EXC_NM));
> + vmcb->_exception_intercepts = HVM_TRAP_MASK;
Just an observation. This handles HAP vs Shadow differently to the
Intel side. I expect we might want to bring them back in line in due
course.
~Andrew
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