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Re: [Xen-devel] [PATCH 1/3] x86/HVM: limit writes to incoming TSS during task switch



>>> On 22.11.16 at 17:32, <andrew.cooper3@xxxxxxxxxx> wrote:
> On 22/11/16 13:55, Jan Beulich wrote:
>> The only field modified (and even that conditionally) is the back link.
>> Write only that field, and only when it actually has been written to.
>>
>> Take the opportunity and also ditch the pointless initializer from the
>> "tss" local variable.
> 
> It would help to point out that tss is unconditionally filled completely
> from guest memory.
> 
>> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
> 
> As for the mechanical adjustments here, Reviewed-by: Andrew Cooper
> <andrew.cooper3@xxxxxxxxxx>
> 
> However, is the position of the backlink write actually correct?  I'd
> have thought that all access to the old tss happen before switching cr3.

But the backlink gets written into the incoming TSS. And I think it
is being assumed anyway that both TSSes (just like the GDT) are
visible through either CR3, the more that the incoming TSS
necessarily is being read in the old address space context.

Jan


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