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Re: [PATCH v2 3/7] x86/ucode/intel: Remove gratuitous memory allocations from cpu_request_microcode()

  • To: Jan Beulich <jbeulich@xxxxxxxx>
  • From: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
  • Date: Tue, 31 Mar 2020 15:17:06 +0100
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  • Cc: Xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxxx>, Wei Liu <wl@xxxxxxx>, Roger Pau Monné <roger.pau@xxxxxxxxxx>
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On 31/03/2020 15:09, Jan Beulich wrote:
> On 27.03.2020 13:28, Andrew Cooper wrote:
>> cpu_request_microcode() needs to scan its container and duplicate one blob,
>> but the get_next_ucode_from_buffer() helper duplicates every blob in turn.
>> Furthermore, the length checking is only safe from overflow in 64bit builds.
>> Delete get_next_ucode_from_buffer() and alter the purpose of the saved
>> variable to simply point somewhere in buf until we're ready to return.
>> This is only a modest reduction in absolute code size (-144), but avoids
>> making memory allocations for every blob in the container.
>> Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
> Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
>> v2:
>>  * Rebase over struct microcode_patch re-work
>>  * Reinstate printk() for bad data
> Ooi, did the number mentioned above indeed no change with this?
> (I don't mean you to adjust it, as it's precise value is not
> really meaningful anyway without also knowing compiler version
> etc.)

I actually stripped the number after re-reading this on xen-devel.  I
didn't go back to check, but it almost certainly isn't the same.




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