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Re: [PATCH 06/22] x86: map/unmap pages in restore_all_guests
- To: Julien Grall <julien@xxxxxxx>
- From: Jan Beulich <jbeulich@xxxxxxxx>
- Date: Thu, 22 Dec 2022 12:12:26 +0100
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- Cc: Hongyan Xia <hongyxia@xxxxxxxxxx>, Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, Roger Pau Monné <roger.pau@xxxxxxxxxx>, Wei Liu <wl@xxxxxxx>, Julien Grall <jgrall@xxxxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxxx
- Delivery-date: Thu, 22 Dec 2022 11:12:49 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 16.12.2022 12:48, Julien Grall wrote:
> --- a/xen/arch/x86/x86_64/entry.S
> +++ b/xen/arch/x86/x86_64/entry.S
> @@ -165,7 +165,24 @@ restore_all_guest:
> and %rsi, %rdi
> and %r9, %rsi
> add %rcx, %rdi
> - add %rcx, %rsi
> +
> + /*
> + * Without a direct map, we have to map first before copying. We
> only
> + * need to map the guest root table but not the per-CPU root_pgt,
> + * because the latter is still a xenheap page.
> + */
> + pushq %r9
> + pushq %rdx
> + pushq %rax
> + pushq %rdi
> + mov %rsi, %rdi
> + shr $PAGE_SHIFT, %rdi
> + callq map_domain_page
> + mov %rax, %rsi
> + popq %rdi
> + /* Stash the pointer for unmapping later. */
> + pushq %rax
> +
> mov $ROOT_PAGETABLE_FIRST_XEN_SLOT, %ecx
> mov root_table_offset(SH_LINEAR_PT_VIRT_START)*8(%rsi), %r8
> mov %r8, root_table_offset(SH_LINEAR_PT_VIRT_START)*8(%rdi)
> @@ -177,6 +194,14 @@ restore_all_guest:
> sub $(ROOT_PAGETABLE_FIRST_XEN_SLOT - \
> ROOT_PAGETABLE_LAST_XEN_SLOT - 1) * 8, %rdi
> rep movsq
> +
> + /* Unmap the page. */
> + popq %rdi
> + callq unmap_domain_page
> + popq %rax
> + popq %rdx
> + popq %r9
While the PUSH/POP are part of what I dislike here, I think this wants
doing differently: Establish a mapping when putting in place a new guest
page table, and use the pointer here. This could be a new per-domain
mapping, to limit its visibility.
Jan
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