Re: [Xen-devel] [PATCH v2] x86/vm_event: add gdtr_base to the vm_event structure

[Tamas K Lengyel <tamas@xxxxxxxxxxxxx>]

On Thu, May 2, 2019 at 5:42 PM Andrew Cooper <andrew.cooper3@xxxxxxxxxx> wrote:
>
> On 02/05/2019 23:40, Tamas K Lengyel wrote:
> >> @@ -211,13 +212,14 @@ struct vm_event_regs_x86 {
> >>      struct vm_event_x86_selector_reg fs;
> >>      struct vm_event_x86_selector_reg gs;
> >>      uint64_t shadow_gs;
> >> +    uint16_t gdtr_limit;
> > Whoops, just noticed that limit actually needs 20-bits. I'll just grow
> > this to 32 and drop the pad at the end.
>
> There is no such thing as a GDT or an IDT with a limit beyond 16 bits.
> (Furthermore, an IDT with a limit beyond 12 bits is just a waste of memory).
>
> VT-x performs a consistency check on every vmentry that the
> VMCS_{G,I}DTR_LIMIT fields are within 16 bits, despite being encoded as
> 32bit fields.  SVM specifies the higher 16 bits as ignored.
>

Thanks for the clarification - in that case v2 of this patch is correct.

Tamas

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