linux-kernel - Re: [PATCH v2 4/7] s390/physmem_info: query diag500(STORAGE LIMIT) to support QEMU/KVM memory devices

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <45de474c-9af3-4d71-959f-6dbc223b432b@redhat.com>
Date: Thu, 17 Oct 2024 14:07:12 +0200
From: David Hildenbrand <david@...hat.com>
To: Alexander Gordeev <agordeev@...ux.ibm.com>
Cc: linux-kernel@...r.kernel.org, linux-mm@...ck.org,
 linux-s390@...r.kernel.org, virtualization@...ts.linux.dev,
 linux-doc@...r.kernel.org, kvm@...r.kernel.org,
 Heiko Carstens <hca@...ux.ibm.com>, Vasily Gorbik <gor@...ux.ibm.com>,
 Christian Borntraeger <borntraeger@...ux.ibm.com>,
 Sven Schnelle <svens@...ux.ibm.com>, Thomas Huth <thuth@...hat.com>,
 Cornelia Huck <cohuck@...hat.com>, Janosch Frank <frankja@...ux.ibm.com>,
 Claudio Imbrenda <imbrenda@...ux.ibm.com>,
 "Michael S. Tsirkin" <mst@...hat.com>, Jason Wang <jasowang@...hat.com>,
 Xuan Zhuo <xuanzhuo@...ux.alibaba.com>, Eugenio Pérez
 <eperezma@...hat.com>, Andrew Morton <akpm@...ux-foundation.org>,
 Jonathan Corbet <corbet@....net>, Mario Casquero <mcasquer@...hat.com>
Subject: Re: [PATCH v2 4/7] s390/physmem_info: query diag500(STORAGE LIMIT) to
 support QEMU/KVM memory devices

On 17.10.24 12:00, David Hildenbrand wrote:
> On 17.10.24 11:53, Alexander Gordeev wrote:
>>>> Why search_mem_end() is not tried in case sclp_early_get_memsize() failed?
>>>
>>> Patch #3 documents that:
>>>
>>> +    The storage limit does not indicate currently usable storage, it may
>>> +    include holes, standby storage and areas reserved for other means, such
>>> +    as memory hotplug or virtio-mem devices. Other interfaces for detecting
>>> +    actually usable storage, such as SCLP, must be used in conjunction with
>>> +    this subfunction.
>>
>> Yes, I read this and that exactly what causes my confusion. In this wording it
>> sounds like SCLP *or* other methods are fine to use. But then you use SCLP or
>> DIAGNOSE 260, but not memory scanning. So I am still confused ;)
> 
> Well, DIAGNOSE 260 is z/VM only and DIAG 500 is KVM only. So there are
> currently not really any other reasonable ways besides SCLP.

Correction: Staring at the code again, in detect_physmem_online_ranges()
we will indeed try:

a) sclp_early_read_storage_info()
b) diag260()

But if neither works, we cannot blindly add all that memory, something is
messed up. So we'll fallback to

c) sclp_early_get_memsize()

But if none of that works, something is seriously wrong.

I will squash the following:

diff --git a/arch/s390/boot/physmem_info.c b/arch/s390/boot/physmem_info.c
index 975fc478e0e3..6ad3ac2050eb 100644
--- a/arch/s390/boot/physmem_info.c
+++ b/arch/s390/boot/physmem_info.c
@@ -214,6 +214,12 @@ void detect_physmem_online_ranges(unsigned long max_physmem_end)
                 return;
         } else if (physmem_info.info_source == MEM_DETECT_DIAG500_STOR_LIMIT) {
                 max_physmem_end = 0;
+               /*
+                * If we know the storage limit but do not find any other
+                * indication of usable initial memory, something is messed
+                * up. In that case, we'll not add any physical memory so
+                * we'll run into die_oom() later.
+                */
                 if (!sclp_early_get_memsize(&max_physmem_end))
                         physmem_info.info_source = MEM_DETECT_SCLP_READ_INFO;
         }

-- 
Cheers,

David / dhildenb