Re: [Xen-devel] [PATCH for-4.11] x86/VT-x: Fix determination of EFER.LMA in vmcs_dump_vcpu()

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 09.04.18 at 19:56, <andrew.cooper3@xxxxxxxxxx> wrote:
> --- a/xen/arch/x86/hvm/vmx/vmcs.c
> +++ b/xen/arch/x86/hvm/vmx/vmcs.c
> @@ -1788,7 +1788,10 @@ void vmcs_dump_vcpu(struct vcpu *v)
>      vmentry_ctl = vmr32(VM_ENTRY_CONTROLS),
>      vmexit_ctl = vmr32(VM_EXIT_CONTROLS);
>      cr4 = vmr(GUEST_CR4);
> -    efer = vmr(GUEST_EFER);
> +
> +    /* EFER.LMA is read as zero, and is loaded from vmentry_ctl on entry. */
> +    BUILD_BUG_ON(VM_ENTRY_IA32E_MODE << 1 != EFER_LMA);
> +    efer = vmr(GUEST_EFER) | ((vmentry_ctl & VM_ENTRY_IA32E_MODE) << 1);

I have to admit that - despite the BUILD_BUG_ON() - I dislike the
literal 1 here, which would better be
(_EFER_LMA - _VM_ENTRY_IA32E_MODE), albeit the latter doesn't
exist, so perhaps

    efer = vmr(GUEST_EFER) | ((vmentry_ctl & VM_ENTRY_IA32E_MODE) * (EFER_LMA / 
VM_ENTRY_IA32E_MODE));

or the same expressed through MASK_EXTR() / MASK_INSR()? But
it's the VMX maintainers to judge anyway.

Jan


_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxxxxxxxxx
https://lists.xenproject.org/mailman/listinfo/xen-devel