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

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Message-ID: <f05056e6-77a7-d0f5-615e-36efaab3ff05@redhat.com>
Date:   Mon, 11 Sep 2023 16:33:48 +0200
From:   David Hildenbrand <david@...hat.com>
To:     "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
Cc:     Adrian Hunter <adrian.hunter@...el.com>,
        Borislav Petkov <bp@...en8.de>,
        Andrew Morton <akpm@...ux-foundation.org>,
        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 11.09.23 12:05, Kirill A. Shutemov wrote:
> On Mon, Sep 11, 2023 at 11:50:31AM +0200, David Hildenbrand wrote:
>> On 11.09.23 11:27, Kirill A. Shutemov wrote:
>>> On Mon, Sep 11, 2023 at 10:42:51AM +0200, David Hildenbrand wrote:
>>>> On 11.09.23 10:41, Kirill A. Shutemov wrote:
>>>>> On Mon, Sep 11, 2023 at 10:03:36AM +0200, David Hildenbrand wrote:
>>>>>> 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)?
>>>>>
>>>>> There are few patches in my queue to few related issue, but generally,
>>>>> yes, the information is available to the target kernel via EFI
>>>>> configuration table.
>>>>
>>>> I assume that table provided by the first kernel, and not read directly from
>>>> HW, correct?
>>>
>>> The table is constructed by the EFI stub in the first kernel based on EFI
>>> memory map.
>>>
>>
>> Okay, should work then once that's done by the first kernel.
>>
>> Maybe include this patch in your series?
> 
> Can do. But the other two patches are not related to kexec. Hm.

Yes, the others can go in separately. But this here really needs other 
kexec/kdump changes.

-- 
Cheers,

David / dhildenb