Re: [Xen-devel] [PATCH v2 2/4] x86/microcode: avoid unnecessary xmalloc/memcpy of ucode data

[Eslam Elnikety <elnikety@amazon.com>]

On 18.12.19 13:05, Jan Beulich wrote:
> On 18.12.2019 02:32, Eslam Elnikety wrote:
>> @@ -725,7 +701,7 @@ static int __init microcode_init(void)
>>        */
>>       if ( ucode_blob.size )
>>       {
>> -        xfree(ucode_blob.data);
>> +        bootstrap_map(NULL);
> 
> As much as I like the change, I wholeheartedly disagree with this
> aspect of it: You make it largely unpredictable when the boot
> mappings will go away - it becomes entirely dependent upon link
> order. And of course we really want these mappings to be gone,
> the very latest (I think), by the time we start bringing up APs
> (but generally the sooner the better). This is (one of?) the main
> reason(s) why it hadn't been done this way to begin with. The
> alternative is more complicated (set up a proper, long term
> mapping), but it's going to be more clean (including the mapping
> then also being suitable to post-boot CPU onlining).
> 

This change is an improvement on the current status. We get to avoid 
xmalloc/memcpy in the case of a successful ucode=scan. The problematic 
aspect you highlight is anyway there regardless of this patch (ref. to 
the "else if ( ucode_mod.mod_end )" in microcode_init). The proper, long 
term mapping would be a welcome change, but is otherwise independent of 
this patch imo.

Thanks,
Eslam

_______________________________________________
Xen-devel mailing list
Xen-devel@lists.xenproject.org
https://lists.xenproject.org/mailman/listinfo/xen-devel