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Re: [PATCH v4 3/5] x86: extend do_mmu_update() to support returning the old PTE value
- To: Kevin Lampis <kevin.lampis@xxxxxxxxxx>
- From: Jan Beulich <jbeulich@xxxxxxxx>
- Date: Tue, 10 Nov 2026 10:14:15 +0100
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- Cc: andrew.cooper3@xxxxxxxxxx, roger@xxxxxxxxxxxxxx, teddy.astie@xxxxxxxxxx, xen-devel@xxxxxxxxxxxxxxxxxxxx
- Delivery-date: Tue, 10 Nov 2026 09:14:28 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 16.10.2026 18:48, Kevin Lampis wrote:
> @@ -4212,37 +4213,80 @@ long do_mmu_update(
> update_flags = PTE_UPDATE_PRESERVE_AD;
> else if ( cmd == MMU_PT_UPDATE_NO_TRANSLATE )
> update_flags = PTE_UPDATE_NO_TRANSLATE;
> + else if ( cmd == MMU_PT_UPDATE_SWAP )
> + update_flags = PTE_UPDATE_SWAP;
>
> switch ( page->u.inuse.type_info & PGT_type_mask )
> {
> case PGT_l1_page_table:
> + l1_pgentry_t ol1e = {};
> rc = mod_l1_entry(va, l1e_from_intpte(req.val), mfn,
> - update_flags, v, pg_owner, NULL);
> + update_flags, v, pg_owner, &ol1e);
> +
> + if ( !rc && cmd == MMU_PT_UPDATE_SWAP )
> + {
> + req.val = ol1e.l1;
> + if ( unlikely(copy_to_guest(ureqs, &req, 1)) )
> + rc = -EFAULT;
Because of the earlier copy_from_guest(), __copy_to_guest() will do here. Also
you only mean to copy back .val, so __copy_field_to_guest() is all you need.
(Same further down, obviously.)
Jan
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