Re: [PATCH] x86/traps: 'Fix' safety of read_registers() in #DF path

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 16/10/2020 12:55, Jan Beulich wrote:
> On 16.10.2020 13:24, Andrew Cooper wrote:
>> On a tangent, what are your views WRT backport beyond 4.14?
>>
>> Back then, it was #DB which was adjacent to the guard frame (which was
>> not present), but it doesn't use show_registers() by default, so I think
>> the problem is mostly hidden.
> I wasn't fully decided yet, but as long as it applies reasonably
> cleanly I think I'm leaning towards also putting it on 4.13.
> 4.12 closes anyway once 4.12.4 is out, and I don't think I want
> to pick up not-really-urgent changes for putting there beyond
> the few ones that I already have (and that I mean to put in
> alongside the XSA fixes on Tuesday); I could be talked into it,
> though.

The question I was asking was really "should I try and make an
equivalent fix for 4.13 and older".

While the base premise of the fix would be the same, the logic in
load_system_tables() is different, and the commit message is completely
wrong.

I only encountered this problem with added instrumentation in the #DB
handler, which is why I'm questioning the utility of going to this effort.

~Andrew