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Re: [PATCH v2 3/7] x86: extend update_intpte() to support atomic get-and-update
- To: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxxx>
- From: Kevin Lampis <kevin.lampis@xxxxxxxxxx>
- Date: Tue, 15 Sep 2026 19:37:25 +0000
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- Cc: "jbeulich@xxxxxxxx" <jbeulich@xxxxxxxx>, "teddy.astie@xxxxxxxxxx" <teddy.astie@xxxxxxxxxx>
- Delivery-date: Tue, 15 Sep 2026 19:37:43 +0000
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- Thread-topic: [PATCH v2 3/7] x86: extend update_intpte() to support atomic get-and-update
>This seems unwise. I think you want a return 0 in the
>paging_write_guest_entry() case because returning the input cannot
>possibly lead to anything good.
This would make the calling code in mod_l1_entry() more complicated.
At the moment it shakes out like this
static int mod_l1_entry(l1_pgentry_t *pl1e,
...,
l1_pgentry_t *ol1e_out)
{
l1_pgentry_t ol1e = l1e_read(pl1e);
...
ol1e = UPDATE_ENTRY(l1, pl1e, ol1e, ...);
...
put_page_from_l1e(ol1e, pt_dom);
...
if ( ol1e_out )
*ol1e_out = ol1e;
}
But if UPDATE_ENTRY() sometimes returns 0 depending on what internal path it
takes then we'll need two local ol1e variables, one that is always valid to
give to put_page_from_l1e() and a different one to maybe assign to *ol1e_out.
When you say "returning the input cannot possibly lead to anything good", the
current version of this patch series actually depends on it.
I guess I just wanted to clarify before adding more complexity to mod_l1_entry.
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