linux-kernel - Re: [PATCH v3 2/2] s390/mm: re-enable the shared zeropage for !PV and !skeys KVM guests

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Message-ID: <20d1d8c5-70e9-4b00-965b-918f275cfae7@linux.ibm.com>
Date: Tue, 16 Apr 2024 14:02:22 +0200
From: Christian Borntraeger <borntraeger@...ux.ibm.com>
To: Alexander Gordeev <agordeev@...ux.ibm.com>,
        David Hildenbrand <david@...hat.com>
Cc: linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        Janosch Frank <frankja@...ux.ibm.com>,
        Claudio Imbrenda <imbrenda@...ux.ibm.com>,
        Heiko Carstens
 <hca@...ux.ibm.com>, Vasily Gorbik <gor@...ux.ibm.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Peter Xu <peterx@...hat.com>, Sven Schnelle <svens@...ux.ibm.com>,
        Gerald Schaefer <gerald.schaefer@...ux.ibm.com>,
        Andrea Arcangeli <aarcange@...hat.com>, kvm@...r.kernel.org,
        linux-s390@...r.kernel.org
Subject: Re: [PATCH v3 2/2] s390/mm: re-enable the shared zeropage for !PV and
 !skeys KVM guests



Am 16.04.24 um 08:37 schrieb Alexander Gordeev:

>> We could piggy-back on vm_fault_to_errno(). We could use
>> vm_fault_to_errno(rc, FOLL_HWPOISON), and only continue (retry) if the rc is 0 or
>> -EFAULT, otherwise fail with the returned error.
>>
>> But I'd do that as a follow up, and also use it in break_ksm() in the same fashion.
> 
> @Christian, do you agree with this suggestion?

I would need to look into that more closely to give a proper answer. In general I am ok
with this but I prefer to have more eyes on that.
 From what I can tell we should cover all the normal cases with our CI as soon as it hits
next. But maybe we should try to create/change a selftest to trigger these error cases?