linux-kernel - Re: [PATCH v5 08/23] KVM: s390: KVM page table management functions: allocation

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Message-ID: <e01dbad3-1684-4d90-a72d-248eb3488bc2@linux.ibm.com>
Date: Mon, 24 Nov 2025 14:01:10 +0100
From: Janosch Frank <frankja@...ux.ibm.com>
To: Claudio Imbrenda <imbrenda@...ux.ibm.com>
Cc: kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-s390@...r.kernel.org, borntraeger@...ibm.com, nsg@...ux.ibm.com,
        nrb@...ux.ibm.com, seiden@...ux.ibm.com, gra@...ux.ibm.com,
        schlameuss@...ux.ibm.com, hca@...ux.ibm.com, svens@...ux.ibm.com,
        agordeev@...ux.ibm.com, gor@...ux.ibm.com, david@...hat.com,
        gerald.schaefer@...ux.ibm.com
Subject: Re: [PATCH v5 08/23] KVM: s390: KVM page table management functions:
 allocation

On 11/24/25 13:41, Claudio Imbrenda wrote:
> On Mon, 24 Nov 2025 13:27:24 +0100
> Janosch Frank <frankja@...ux.ibm.com> wrote:
> 
>> On 11/24/25 12:55, Claudio Imbrenda wrote:
>>> Add page table management functions to be used for KVM guest (gmap)
>>> page tables.
>>>
>>> This patch adds the boilerplate and functions for the allocation and
>>> deallocation of DAT tables.
>>>
>>> Signed-off-by: Claudio Imbrenda <imbrenda@...ux.ibm.com>
>>
>> What's the cache for, why did you add it?
> 
> the cache is needed to allocate memory when we can sleep (to avoid
> atomic allocations), and use it when holding spinlocks (when we can't
> sleep).
> 
> this is similar to what other architectures do, except that in their
> case they only have one type of page table to worry about, we need at
> least 3 types of objects.
> 
> unlike other architectures, allocations from the cache can fail, and
> the calling code needs to handle failures (e.g. by replenishing the
> cache and trying again)

Well, this information should make it into this patch, either into the 
description or in the body.

> 
>>
>>> ---
>>>    arch/s390/kvm/Makefile     |   1 +
>>>    arch/s390/kvm/dat.c        | 103 +++++++++++++++++++++++++++++++++++++
>>>    arch/s390/kvm/dat.h        |  77 +++++++++++++++++++++++++++
>>>    arch/s390/mm/page-states.c |   1 +
>>>    4 files changed, 182 insertions(+)
>>>    create mode 100644 arch/s390/kvm/dat.c