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Date:   Wed, 1 Jun 2022 17:46:54 +0300
From:   "Kirill A. Shutemov" <kirill@shutemov.name>
To:     David Hildenbrand <david@redhat.com>
Cc:     "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
        Borislav Petkov <bp@alien8.de>,
        Andy Lutomirski <luto@kernel.org>,
        Sean Christopherson <seanjc@google.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Joerg Roedel <jroedel@suse.de>,
        Ard Biesheuvel <ardb@kernel.org>,
        Andi Kleen <ak@linux.intel.com>,
        Kuppuswamy Sathyanarayanan 
        <sathyanarayanan.kuppuswamy@linux.intel.com>,
        David Rientjes <rientjes@google.com>,
        Vlastimil Babka <vbabka@suse.cz>,
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        Varad Gautam <varad.gautam@suse.com>,
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        Dave Hansen <dave.hansen@intel.com>,
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Subject: Re: [PATCHv6 03/15] efi/x86: Get full memory map in allocate_e820()
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On Wed, Jun 01, 2022 at 04:39:16PM +0200, David Hildenbrand wrote:
> On 01.06.22 16:35, Kirill A. Shutemov wrote:
> > On Wed, Jun 01, 2022 at 11:00:23AM +0200, David Hildenbrand wrote:
> >> On 17.05.22 17:34, Kirill A. Shutemov wrote:
> >>> Currently allocate_e820() only interested in the size of map and size of
> >>> memory descriptor to determine how many e820 entries the kernel needs.
> >>>
> >>> UEFI Specification version 2.9 introduces a new memory type --
> >>> unaccepted memory. To track unaccepted memory kernel needs to allocate
> >>> a bitmap. The size of the bitmap is dependent on the maximum physical
> >>> address present in the system. A full memory map is required to find
> >>> the maximum address.
> >>>
> >>> Modify allocate_e820() to get a full memory map.
> >>
> >> Usually we use max_pfn, if we want to know the maximum pfn that's
> >> present in the system (well, IIRC, excluding hotunplug).
> >>
> >> How exactly will this (different?) maximum from UEFI for the bitmap
> >> interact with
> >>
> >> max_pfn = e820__end_of_ram_pfn();
> >>
> >> from e820 in existing code
> >>
> >> ?
> > 
> > I'm not sure I understand the question.
> 
> Essentially, if the PFN you calculate here for the bitmap size will
> essentially match later max_pfn.

Yes, generally. But is can decrease if kernel transit memory from TYPE_RAM
to TYPE_RESERVE. In any case we will not step out of the allocated bitmap.

-- 
 Kirill A. Shutemov