linux-kernel - Re: [PATCH V2 1/2] efi/unaccepted: Do not let /proc/vmcore try to access unaccepted memory

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Message-ID: <1c736ca3-36e2-3225-2f98-e51149c468ef@intel.com>
Date:   Tue, 12 Sep 2023 10:47:49 +0300
From:   Adrian Hunter <adrian.hunter@...el.com>
To:     David Hildenbrand <david@...hat.com>,
        Adrian Hunter <adrian.hunter@...el.com>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Borislav Petkov <bp@...en8.de>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Ard Biesheuvel <ardb@...nel.org>
Cc:     Dave Hansen <dave.hansen@...el.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        Mike Rapoport <rppt@...ux.ibm.com>,
        Lorenzo Stoakes <lstoakes@...il.com>,
        Tom Lendacky <thomas.lendacky@....com>,
        Baoquan He <bhe@...hat.com>, Vivek Goyal <vgoyal@...hat.com>,
        Dave Young <dyoung@...hat.com>, linux-kernel@...r.kernel.org,
        linux-fsdevel@...r.kernel.org, linux-mm@...ck.org,
        linux-coco@...ts.linux.dev, linux-efi@...r.kernel.org,
        kexec@...ts.infradead.org
Subject: Re: [PATCH V2 1/2] efi/unaccepted: Do not let /proc/vmcore try to
 access unaccepted memory

On 12/09/23 10:19, David Hildenbrand wrote:
> On 11.09.23 13:21, Adrian Hunter wrote:
>> Support for unaccepted memory was added recently, refer commit dcdfdd40fa82
>> ("mm: Add support for unaccepted memory"), whereby a virtual machine may
>> need to accept memory before it can be used.
>>
>> Do not let /proc/vmcore try to access unaccepted memory because it can
>> cause the guest to fail.
> 
> Oh, hold on. What are the actual side effects of this?
> 
> Once we're in the kdump kernel, any guest is already dead. So failing a guest doesn't apply, no?
> 
Unaccepted Memory is used by virtual machines.  In this case the guest
has kexec'ed to a dump-capture kernel, so the virtual machine is still
alive and running the dump-capture kernel.