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Re: [PATCH] x86/platform: fix the MTRR rollback in XENPF_add_memtype
- To: Yuho Choi <oss.patchbox@xxxxxxxxx>
- From: Jan Beulich <jbeulich@xxxxxxxx>
- Date: Wed, 4 Nov 2026 07:37:48 +0100
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- Cc: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, Roger Pau Monné <roger@xxxxxxxxxxxxxx>, Teddy Astie <teddy.astie@xxxxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxxx
- Delivery-date: Wed, 04 Nov 2026 06:37:55 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 04.11.2026 05:50, Yuho Choi wrote:
> If copying the result back to the caller fails, XENPF_add_memtype
> tries to undo mtrr_add_page() with mtrr_del_page(ret, 0, 0). By then
> ret holds -EFAULT, so mtrr_del_page() looks up an MTRR with base and
> size 0 and releases nothing. The register that was added, or whose
> usage count was raised, stays in use, and the caller only gets
> -EFAULT, without the register number it would need to delete it.
>
> Pass the register number saved in op->u.add_memtype.reg instead.
>
> Fixes: 8ee614278c2d ("[XEN] Fix memtype accessor domctls.")
> Signed-off-by: Yuho Choi <oss.patchbox@xxxxxxxxx>
Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
for the immediate purpose. However, I wonder if we shouldn't drop the
rollback. Elsewhere when the final copy-out of a hypercall fails, we
don't do any such rollback.
Jan
> --- a/xen/arch/x86/platform_hypercall.c
> +++ b/xen/arch/x86/platform_hypercall.c
> @@ -295,7 +295,7 @@ ret_t do_platform_op(
> ret = __copy_field_to_guest(u_xenpf_op, op, u.add_memtype) ?
> -EFAULT : 0;
> if ( ret != 0 )
> - mtrr_del_page(ret, 0, 0);
> + mtrr_del_page(op->u.add_memtype.reg, 0, 0);
> }
> break;
>
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