linux-kernel - Re: [PATCH 1/3] proc/vmcore: Do not map unaccepted memory

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Message-ID: <ef97f466-b27a-a883-7131-c2051480dd87@redhat.com>
Date:   Mon, 11 Sep 2023 10:03:36 +0200
From:   David Hildenbrand <david@...hat.com>
To:     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>
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 1/3] proc/vmcore: Do not map unaccepted memory

On 06.09.23 09:39, 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 map unaccepted memory because it can cause the guest to fail.
> 
> For /proc/vmcore, which is read-only, this means a read or mmap of
> unaccepted memory will return zeros.

Does a second (kdump) kernel that exposes /proc/vmcore reliably get 
access to the information whether memory of the first kernel is 
unaccepted (IOW, not its memory, but the memory of the first kernel it 
is supposed to expose via /proc/vmcore)?

I recall there might be other kdump-related issues for TDX and friends 
to solve. Especially, which information the second kernel gets provided 
by the first kernel.

So can this patch even be tested reasonably (IOW, get into a kdump 
kernel in an environment where the first kernel has unaccepted memory, 
and verify that unaccepted memory is handled accordingly? ... while 
kdump doing anything reasonable in such an environment at all?)

-- 
Cheers,

David / dhildenb