On Tue, Feb 03, 2026 at 11:10:17AM +0100, 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.
>
> Limit the allocation address restriction to 32bit PV guests only.
>
> 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 <[email protected]>
> ---
> xen/arch/x86/domain.c | 9 ++++++---
> 1 file changed, 6 insertions(+), 3 deletions(-)
>
> diff --git a/xen/arch/x86/domain.c b/xen/arch/x86/domain.c
> index edb76366b596..4163568043b1 100644
> --- a/xen/arch/x86/domain.c
> +++ b/xen/arch/x86/domain.c
> @@ -882,10 +882,13 @@ int arch_domain_create(struct domain *d,
> goto fail;
>
> /*
> - * The shared_info machine address must fit in a 32-bit field within a
> - * 32-bit guest's start_info structure. Hence we specify MEMF_bits(32).
> + * For 32bit PV guests the shared_info machine address must fit in a
> 32-bit
> + * field within the guest's start_info structure. Hence we specify
> + * MEMF_bits(32).
> */
> - if ( (d->shared_info = alloc_xenheap_pages(0, MEMF_bits(32))) == NULL )
> + if ( (d->shared_info =
> + alloc_xenheap_pages(0, is_pv_32bit_domain(d) ? MEMF_bits(32)
> + : 0)) == NULL )
Sorry, this is wrong, it's too early to know whether the domain is 32
or 64bit.
Roger.
