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Re: [PATCH] x86/shadow: Drop dubious lastpage diagnostic


  • To: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
  • From: Jan Beulich <jbeulich@xxxxxxxx>
  • Date: Fri, 20 Jan 2023 14:10:56 +0100
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  • Cc: Roger Pau Monné <roger.pau@xxxxxxxxxx>, Wei Liu <wl@xxxxxxx>, George Dunlap <george.dunlap@xxxxxxxxxxxxx>, Tim Deegan <tim@xxxxxxx>, Xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxxx>
  • Delivery-date: Fri, 20 Jan 2023 13:11:44 +0000
  • List-id: Xen developer discussion <xen-devel.lists.xenproject.org>

On 20.01.2023 12:45, Andrew Cooper wrote:
> This is a global variable (actually 3, one per GUEST_PAGING_LEVEL), operated
> on using atomics only (with no regard to what else shares the same cacheline),
> which emits a diagnostic (in debug builds only) without changing any program
> behaviour.
> 
> Based on read-only p2m types including logdirty, this diagnostic can be
> tripped by entirely legitimate guest behaviour.

Can it? At the very least shadow doesn't use p2m_ram_logdirty, but "cooks"
log-dirty handling its own way.

> Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>

Acked-by: Jan Beulich <jbeulich@xxxxxxxx>
with the last sentence above corrected (if need be: removed).

Jan



 


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