Re: [PATCH] x86/altp2m: altp2m_get_effective_entry() should honor ap2m->default_access

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 12/01/2026 11:09 am, Jan Beulich wrote:
> On 09.01.2026 19:28, Petr Beneš wrote:
>> From: Petr Beneš <w1benny@xxxxxxxxx>
>>
>> Commit 7e5b662 fixed p2m_altp2m_get_or_propagate() to use the altp2m's
>> default_access when propagating entries from the host p2m. However, the same
>> fix was not applied to altp2m_get_effective_entry(), which has the same 
>> issue.
>>
>> When altp2m_get_effective_entry() prepopulates a superpage from the host
>> p2m, it incorrectly uses the host p2m's access permissions instead of
>> the altp2m's default_access. This causes problems when the superpage is
>> later split (e.g., when setting mem_access on a specific 4K page): all
>> 512 entries inherit the host p2m's access rights instead of the altp2m's
>> default_access.
>>
>> This issue became apparent after commit 50baf2d, which causes the host p2m
>> to use superpages more frequently. Before that commit, the host p2m
>> typically had 4K entries after VM restore, so the prepopulate branch was
>> rarely taken.
>>
>> Symptoms include memory-access events firing for unexpected pages when
>> using VMI tools with altp2m, particularly after VM resume.
>> The issue can be worked around by booting with "hap_1gb=0 hap_2mb=0".
>>
>> Fixes: 7e5b662 ("x86/altp2m: p2m_altp2m_get_or_propagate() should honor 
>> ap2m->default_access")
> You didn't even Cc Tamas, who I think once again will need to ack this.
> Already with the referenced change I didn't quite understand the
> reasoning.
>
> However, two formal points: Please use 12-digit hashes, as demanded by
> sending-patches.pandoc. Plus I don't think Fixes: is quite right here.
> That earlier change of yours didn't mean to do more than it did, by its
> title and description. We relatively recently introduced Amends:, which
> may be a suitable fit here.

I beg your pardon?  Fixes are and Amends are synonyms.  You cannot use
them like this, and you absolutely cannot expect contributors to know
your personal interpretation of the words.

~Andrew