linux-kernel - Re: [PATCH v7 1/3] efi/x86: Fix EFI memory map corruption with kexec

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Date: Tue, 4 Jun 2024 21:08:55 -0500
From: "Kalra, Ashish" <ashish.kalra@....com>
To: Dave Young <dyoung@...hat.com>
Cc: Borislav Petkov <bp@...en8.de>, Mike Rapoport <rppt@...nel.org>,
 tglx@...utronix.de, mingo@...hat.com, dave.hansen@...ux.intel.com,
 x86@...nel.org, rafael@...nel.org, hpa@...or.com, peterz@...radead.org,
 adrian.hunter@...el.com, sathyanarayanan.kuppuswamy@...ux.intel.com,
 jun.nakajima@...el.com, rick.p.edgecombe@...el.com, thomas.lendacky@....com,
 michael.roth@....com, seanjc@...gle.com, kai.huang@...el.com,
 bhe@...hat.com, kirill.shutemov@...ux.intel.com, bdas@...hat.com,
 vkuznets@...hat.com, dionnaglaze@...gle.com, anisinha@...hat.com,
 jroedel@...e.de, ardb@...nel.org, kexec@...ts.infradead.org,
 linux-coco@...ts.linux.dev, linux-kernel@...r.kernel.org,
 dan.j.williams@...el.com
Subject: Re: [PATCH v7 1/3] efi/x86: Fix EFI memory map corruption with kexec

Hello Dave,

On 6/4/2024 8:58 PM, Dave Young wrote:
> On Wed, 5 Jun 2024 at 09:52, Dave Young <dyoung@...hat.com> wrote:
>>>>         ...
>>>>         if (efi.memmap.flags & (EFI_MEMMAP_MEMBLOCK | EFI_MEMMAP_SLAB)) {
>>>>                 __efi_memmap_free(efi.memmap.phys_map,
>>>>                                 efi.memmap.desc_size * efi.memmap.nr_map, efi.memmap.flags);
>>>>         }
>>> From your debugging the memmap should not be freed.  This piece of
>>> code was added in below commit,  added Dan Williams in cc list:
>>> commit f0ef6523475f18ccd213e22ee593dfd131a2c5ea
>>> Author: Dan Williams <dan.j.williams@...el.com>
>>> Date:   Mon Jan 13 18:22:44 2020 +0100
>>>
>>>     efi: Fix efi_memmap_alloc() leaks
>>>
>>>     With efi_fake_memmap() and efi_arch_mem_reserve() the efi table may be
>>>     updated and replaced multiple times. When that happens a previous
>>>     dynamically allocated efi memory map can be garbage collected. Use the
>>>     new EFI_MEMMAP_{SLAB,MEMBLOCK} flags to detect when a dynamically
>>>     allocated memory map is being replaced.
>>>
>> Dan, probably those regions should be freed only for "fake" memmap?
> Ashish, can you comment out the __efi_memmap_free see if it works for
> you just confirm about the behavior.

Yes, i have already tried and tested that, if i avoid __efi_memmap_free(), then i don't see this memory map corruption.

Thanks, Ashish