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Re: [PATCH v2] x86/domain: adjust limitation on shared_info allocation below 4G
- To: Jan Beulich <jbeulich@xxxxxxxx>
- From: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
- Date: Wed, 4 Feb 2026 16:10:42 +0100
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- Cc: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, Anthony PERARD <anthony.perard@xxxxxxxxxx>, Michal Orzel <michal.orzel@xxxxxxx>, Julien Grall <julien@xxxxxxx>, Stefano Stabellini <sstabellini@xxxxxxxxxx>, Roger Pau Monne <roger.pau@xxxxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxxx
- Delivery-date: Wed, 04 Feb 2026 15:11:10 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 04/02/2026 2:40 pm, Jan Beulich wrote:
>>> + if ( virt_to_maddr(d->shared_info) >> 32 )
>>> + {
>>> + shared_info_t *prev = d->shared_info;
>>> +
>>> + d->shared_info = alloc_xenheap_pages(0, MEMF_bits(32));
>>> + if ( !d->shared_info )
>>> + {
>>> + d->shared_info = prev;
>>> + rc = -ENOMEM;
>>> + goto undo_and_fail;
>>> + }
>>> + put_page(virt_to_page(prev));
>>> + clear_page(d->shared_info);
>> I think copy_page() would be more appropriate. That way there are fewer
>> implicit ordering dependencies.
> I'd strongly recommend against copy_page() here. If there was any data in
> there that would need copying, it would need to be done field-wise, using
> the compat xlat machinery. The layouts are different. It may be prudent to
> assert that the original page is still completely zeroed.
Oh, yes. The layouts will be different. Fine.
~Andrew
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