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Re: [RFC PATCH 07/19] xen/domain: Alloc enough pages for VCPU struct
- To: Mykyta Poturai <Mykyta_Poturai@xxxxxxxx>
- From: Jan Beulich <jbeulich@xxxxxxxx>
- Date: Mon, 2 Feb 2026 17:45:51 +0100
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- Cc: "xakep.amatop@xxxxxxxxx" <xakep.amatop@xxxxxxxxx>, Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, Anthony PERARD <anthony.perard@xxxxxxxxxx>, Michal Orzel <michal.orzel@xxxxxxx>, Julien Grall <julien@xxxxxxx>, Roger Pau Monné <roger.pau@xxxxxxxxxx>, Stefano Stabellini <sstabellini@xxxxxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxxx>
- Delivery-date: Mon, 02 Feb 2026 16:46:03 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 02.02.2026 17:14, Mykyta Poturai wrote:
> With introduction of GICv4 the size of struct vcpu can again be more
> than one page. Modify struct vcpu allocation to request enough pages
> again.
>
> Don't reintroduce the MAX_PAGES_PER_VCPU check.
> As per commit b77d774d8274183c2252f5fbc9fa3b3b7022ba06
>> It turns out that beyond efficiency, maybe, there is no real technical
>> reason this struct has to fit in one page
>
> Since there is no technical reason to limit struct vcpu size to one page,
> there also seems to be little reason the fiddle with 1 or 2 page limits.
Before writing this, did you check the recent discussion around the Arm
side change going back to a single page, and the moving of this code to
common/? Any ...
> --- a/xen/common/domain.c
> +++ b/xen/common/domain.c
> @@ -342,18 +342,24 @@ static struct vcpu *alloc_vcpu_struct(const struct
> domain *d)
> # define arch_vcpu_struct_memflags(d) ((void)(d), 0)
> #endif
> struct vcpu *v;
> + unsigned int order = get_order_from_bytes(sizeof(*v));
>
> - BUILD_BUG_ON(sizeof(*v) > PAGE_SIZE);
> - v = alloc_xenheap_pages(0, arch_vcpu_struct_memflags(d));
> + v = alloc_xenheap_pages(order, arch_vcpu_struct_memflags(d));
... non-order-0 allocation is at risk of failing despite there being
ample memory available, if there's heavy fragmentation. I'm sorry, but
without a much better justification this gets a NAK from me.
Jan
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