Re: [Xen-devel] [PATCH] x86/VMX: don't risk corrupting host CR4

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 09/03/18 14:18, Jan Beulich wrote:
> Instead of "syncing" the live value to what mmu_cr4_features has, make
> sure vCPU-s run with the value most recently loaded into %cr4, such that
> after the next VM exit we continue to run with the intended value rather
> than a possibly stale one.
>
> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
> ---
> TBD: Is the conditional really worthwhile, i.e. is the VMWRITE perhaps
>      not meaningfully more expensive than the VMREAD?

Which bits are you worried about here?  We play with %cr4 quite a bit in
PV context, but we shouldn't be changing after boot in HVM context.

~Andrew

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