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Re: [PATCH v1 2/2] domctl: Handle some of XEN_DOMCTL_shadow_op without the domctl lock
- To: Ross Lagerwall <ross.lagerwall@xxxxxxxxxx>
- From: Jan Beulich <jbeulich@xxxxxxxx>
- Date: Thu, 11 Jun 2026 17:02:22 +0200
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- Cc: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, Roger Pau Monné <roger.pau@xxxxxxxxxx>, Teddy Astie <teddy.astie@xxxxxxxxxx>, Anthony PERARD <anthony.perard@xxxxxxxxxx>, Michal Orzel <michal.orzel@xxxxxxx>, Julien Grall <julien@xxxxxxx>, Stefano Stabellini <sstabellini@xxxxxxxxxx>, "Daniel P. Smith" <dpsmith@xxxxxxxxxxxxxxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxxx
- Delivery-date: Thu, 11 Jun 2026 15:02:40 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 09.06.2026 17:15, Ross Lagerwall wrote:
> --- a/xen/arch/x86/mm/paging.c
> +++ b/xen/arch/x86/mm/paging.c
> @@ -746,11 +746,15 @@ long do_paging_domctl_cont(
> ret = xsm_domctl(XSM_OTHER, d, &op);
> if ( !ret )
> {
> - if ( domctl_lock_acquire() )
> + bool lock = !(op.u.shadow_op.op == XEN_DOMCTL_SHADOW_OP_CLEAN ||
> + op.u.shadow_op.op == XEN_DOMCTL_SHADOW_OP_PEEK);
I realize this has been committed already, yet I'd still like to mention
that I never really understood why expressions like this (with a negation
which can easily be avoided:
bool lock = op.u.shadow_op.op != XEN_DOMCTL_SHADOW_OP_CLEAN &&
op.u.shadow_op.op != XEN_DOMCTL_SHADOW_OP_PEEK;
) would be used. Personally I consider such hampering readability. And
no, the other expression (in do_domctl()) being
if ( op->u.shadow_op.op == XEN_DOMCTL_SHADOW_OP_CLEAN ||
op->u.shadow_op.op == XEN_DOMCTL_SHADOW_OP_PEEK )
imo doesn't justify that either: While in the patch they're close
together and hence the analogy can be easily spotted, in the ultimate
source files the two expressions are far apart.
Jan
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