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Re: [PATCH] x86/shim: Simplify compat handling in write_start_info()


  • To: Jan Beulich <jbeulich@xxxxxxxx>
  • From: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
  • Date: Mon, 19 Apr 2021 16:57:04 +0100
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  • Cc: Roger Pau Monné <roger.pau@xxxxxxxxxx>, Wei Liu <wl@xxxxxxx>, Xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxxx>
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On 19/04/2021 16:55, Jan Beulich wrote:
> On 19.04.2021 16:45, Andrew Cooper wrote:
>> Factor out a compat boolean to remove the lfence overhead from multiple
>> is_pv_32bit_domain() calls.
>>
>> For a compat guest, the upper 32 bits of rdx are zero, so there is no need to
>> have any conditional logic at all when mapping the start info page.
> Iirc the contents of the upper halves hold unspecified contents after
> a switch from compat to 64-bit mode. Therefore only with this part of
> the change dropped ...

But we're shim, so will never ever mix compat and non-compat guests.

~Andrew

>
>> Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
> Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
>
> Jan




 


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