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

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Message-ID: <20230911100555.mjjnx3ujnjlaxgsy@box.shutemov.name>
Date:   Mon, 11 Sep 2023 13:05:55 +0300
From:   "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
To:     David Hildenbrand <david@...hat.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 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.

-- 
  Kiryl Shutsemau / Kirill A. Shutemov