linux-kernel - Re: [PATCH v2 1/1] KVM: s390: pv: fix race when making a page secure

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Message-ID: <bab79dbd-64cc-4a58-aba9-bc5fd4d6beca@redhat.com>
Date: Wed, 26 Feb 2025 18:01:04 +0100
From: David Hildenbrand <david@...hat.com>
To: Claudio Imbrenda <imbrenda@...ux.ibm.com>
Cc: kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
 linux-s390@...r.kernel.org, frankja@...ux.ibm.com, borntraeger@...ibm.com,
 nrb@...ux.ibm.com, seiden@...ux.ibm.com, nsg@...ux.ibm.com,
 schlameuss@...ux.ibm.com, hca@...ux.ibm.com
Subject: Re: [PATCH v2 1/1] KVM: s390: pv: fix race when making a page secure

On 26.02.25 17:58, Claudio Imbrenda wrote:
> On Wed, 26 Feb 2025 16:05:11 +0100
> David Hildenbrand <david@...hat.com> wrote:
> 
>>> +int make_hva_secure(struct mm_struct *mm, unsigned long hva, struct uv_cb_header *uvcb)
>>> +{
>>> +	struct folio *folio;
>>> +	spinlock_t *ptelock;
>>> +	pte_t *ptep;
>>> +	int rc;
>>> +
>>> +	ptep = get_locked_valid_pte(mm, hva, &ptelock);
>>> +	if (!ptep)
>>> +		return -ENXIO;
>>
>> You very likely need a pte_write() check we had there before, as you
>> might effectively modify page content by clearing the page.
> 
> it's not really needed, but it doesn't hurt either, I'll add a check

Can you elaborate why it is not needed? Would the HW enforce that 
writability check already?

-- 
Cheers,

David / dhildenb