From: Jan Beulich Date: Mon, 2 Jul 2018 11:12:10 +0000 (+0200) Subject: VMX: don't needlessly write CR4 guest/host mask X-Git-Tag: archive/raspbian/4.14.0+80-gd101b417b7-1+rpi1^2~63^2~3709 X-Git-Url: https://dgit.raspbian.org/?a=commitdiff_plain;h=c2c0f0db02623d9ad1ca70d1f1d759bb76715e47;p=xen.git VMX: don't needlessly write CR4 guest/host mask In shadow mode the field never changes from ~0UL, so there's no need for a VMWRITE (or an update of its cached value). Signed-off-by: Jan Beulich Reviewed-by: Andrew Cooper Acked-by: Kevin Tian --- diff --git a/xen/arch/x86/hvm/vmx/vmx.c b/xen/arch/x86/hvm/vmx/vmx.c index 20a8a69fbe..8e63eb7813 100644 --- a/xen/arch/x86/hvm/vmx/vmx.c +++ b/xen/arch/x86/hvm/vmx/vmx.c @@ -1585,14 +1585,12 @@ static void vmx_update_guest_cr(struct vcpu *v, unsigned int cr, __vmwrite(GUEST_CR4, v->arch.hvm_vcpu.hw_cr[4]); - if ( !paging_mode_hap(v->domain) ) - /* - * Shadow path has not been optimized because it requires - * unconditionally trapping more CR4 bits, at which point the - * performance benefit of doing this is quite dubious. - */ - v->arch.hvm_vmx.cr4_host_mask = ~0UL; - else + /* + * Shadow path has not been optimized because it requires + * unconditionally trapping more CR4 bits, at which point the + * performance benefit of doing this is quite dubious. + */ + if ( paging_mode_hap(v->domain) ) { /* * Update CR4 host mask to only trap when the guest tries to set @@ -1617,8 +1615,9 @@ static void vmx_update_guest_cr(struct vcpu *v, unsigned int cr, /* Add the nested host mask to get the more restrictive one. */ v->arch.hvm_vmx.cr4_host_mask |= get_vvmcs(v, CR4_GUEST_HOST_MASK); + + __vmwrite(CR4_GUEST_HOST_MASK, v->arch.hvm_vmx.cr4_host_mask); } - __vmwrite(CR4_GUEST_HOST_MASK, v->arch.hvm_vmx.cr4_host_mask); break;