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Re: [PATCH] hvf: guard xgetbv call.

From: Roman Bolshakov
Subject: Re: [PATCH] hvf: guard xgetbv call.
Date: Tue, 12 Jan 2021 10:49:07 +0300

On Mon, Jan 11, 2021 at 07:06:22AM -1000, Richard Henderson wrote:
> On 1/10/21 6:31 PM, Roman Bolshakov wrote:
> >> Also, if we're going to put this some place common, forcing the caller to 
> >> do
> >> the cpuid that feeds this, then we should probably make all of the startup
> >> cpuid stuff common as well.
> >>
> > 
> > I proposed the version because all callers of xgetbv instruction already
> > call cpuid before invoking inline xgetbv.
> > 
> >> Note that we'd probably have to use constructor priorities to get that 
> >> right
> >> for util/bufferiszero.c.
> >>
> > 
> > Please correct me if I read this wrong. What you're saying is we should
> > initialize cpuid in constructors and then use cached cpuid ecx in
> > xgetbv() (and drop one argument, respectively)?
> I would have xgetbv and all of the cpuid values cached at startup, and all
> three places would read global variables.

It makes sense, thanks for the clarification.

Do you think it should be part of the change Hill is doing or it might
be a follow-up cleanup patch?


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