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Re: [PATCH v3] x86/domain: adjust limitation on shared_info allocation below 4G
- To: Roger Pau Monne <roger.pau@xxxxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxxx
- From: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
- Date: Thu, 5 Feb 2026 12:13:24 +0000
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- Cc: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, Jan Beulich <jbeulich@xxxxxxxx>, Anthony PERARD <anthony.perard@xxxxxxxxxx>, Michal Orzel <michal.orzel@xxxxxxx>, Julien Grall <julien@xxxxxxx>, Stefano Stabellini <sstabellini@xxxxxxxxxx>
- Delivery-date: Thu, 05 Feb 2026 12:13:44 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 05/02/2026 8:03 am, Roger Pau Monne wrote:
> The limitation of shared_info being allocated below 4G to fit in the
> start_info field only applies to 32bit PV guests. On 64bit PV guests the
> start_info field is 64bits wide. HVM guests don't use start_info at all.
>
> Drop the restriction in arch_domain_create() and instead free and
> re-allocate the page from memory below 4G if needed in switch_compat(),
> when the guest is set to run in 32bit PV mode.
>
> Fixes: 3cadc0469d5c ("x86_64: shared_info must be allocated below 4GB as it
> is advertised to 32-bit guests via a 32-bit machine address field in
> start_info.")
> Signed-off-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
> Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
Reviewed-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
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