Re: [Xen-devel] [PATCH 4/4] SVM: streamline entry.S code

[Keir Fraser <keir.xen@xxxxxxxxx>]

On 26/08/2013 17:20, "Andrew Cooper" <andrew.cooper3@xxxxxxxxxx> wrote:

> Having read the manual several times, I am now more and more confused about
> this.
>  
>  My reading of the AMD programmer manual vol 3 indicates that %rax after VMRUN
> completes will be the host %rax, i.e. VCPU_svm_vmcb_pa.

Yes.

>  However, I cant find anywhere in the code which overwrites regs->rax from
> vmcb->rax, which I would have thought would have thought would cause utter
> devastation in combination with the generic functions working with a
> cpu_user_regs structure.

It's right there in entry.S: 'mov VMCB_rax(%rcx),%rax; mov
%rax,UREGS_rax(%rsp)'

>  The alternative is that %rax after VMRUN is actually the guest %rax, at which
> point the pushes used to do the correct thing, but are now broken by this
> patch clobbering it before being saved.
>  
>  Can someone with more knowledge please confirm?  I really hope I have
> overlooked something in the code.

:)

 -- Keir



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