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Re: [PATCH v1 2/8] x86/vmx: Remove lazy FPU support
- To: Ross Lagerwall <ross.lagerwall@xxxxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxxx
- From: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
- Date: Thu, 19 Mar 2026 16:38:35 +0000
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- Cc: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, Jan Beulich <jbeulich@xxxxxxxx>, Roger Pau Monné <roger.pau@xxxxxxxxxx>
- Delivery-date: Thu, 19 Mar 2026 16:38:49 +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 VMX 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>
> ---
> xen/arch/x86/hvm/vmx/vmcs.c | 8 +--
> xen/arch/x86/hvm/vmx/vmx.c | 70 +------------------------
> xen/arch/x86/hvm/vmx/vvmx.c | 15 +-----
> xen/arch/x86/include/asm/hvm/vmx/vmcs.h | 2 -
> 4 files changed, 5 insertions(+), 90 deletions(-)
>
> diff --git a/xen/arch/x86/hvm/vmx/vmcs.c b/xen/arch/x86/hvm/vmx/vmcs.c
> index c2e7f9aed39f..8e52ef4d497a 100644
> --- a/xen/arch/x86/hvm/vmx/vmcs.c
> +++ b/xen/arch/x86/hvm/vmx/vmcs.c
> @@ -1247,10 +1247,7 @@ static int construct_vmcs(struct vcpu *v)
> __vmwrite(HOST_TR_SELECTOR, TSS_SELECTOR);
>
> /* Host control registers. */
> - v->arch.hvm.vmx.host_cr0 = read_cr0() & ~X86_CR0_TS;
> - if ( !v->arch.fully_eager_fpu )
> - v->arch.hvm.vmx.host_cr0 |= X86_CR0_TS;
> - __vmwrite(HOST_CR0, v->arch.hvm.vmx.host_cr0);
> + __vmwrite(HOST_CR0, read_cr0());
(Not for this patch) but I'm pretty sure there's room to optimise this
further.
CR0 should be constant, both here and in SVM. Reading the active cr0 is
an example of the anti-pattern we need to purge to make nested-virt work
better.
~Andrew
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