linux-kernel - Re: [PATCH v2 2/3] x86/mm: Do not zap page table entries mapping unaccepted memory table during kdump.

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Date: Thu, 21 Mar 2024 16:58:52 +0200
From: "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
To: Ashish Kalra <Ashish.Kalra@....com>
Cc: tglx@...utronix.de, mingo@...hat.com, dave.hansen@...ux.intel.com, 
	rafael@...nel.org, peterz@...radead.org, adrian.hunter@...el.com, 
	sathyanarayanan.kuppuswamy@...ux.intel.com, elena.reshetova@...el.com, jun.nakajima@...el.com, 
	rick.p.edgecombe@...el.com, thomas.lendacky@....com, seanjc@...gle.com, michael.roth@....com, 
	kai.huang@...el.com, bhe@...hat.com, kexec@...ts.infradead.org, 
	linux-coco@...ts.linux.dev, linux-kernel@...r.kernel.org, bdas@...hat.com, 
	vkuznets@...hat.com, dionnaglaze@...gle.com, anisinha@...hat.com, jroedel@...e.de
Subject: Re: [PATCH v2 2/3] x86/mm: Do not zap page table entries mapping
 unaccepted memory table during kdump.

On Mon, Mar 18, 2024 at 07:02:45AM +0000, Ashish Kalra wrote:
> From: Ashish Kalra <ashish.kalra@....com>
> 
> During crashkernel boot only pre-allocated crash memory is presented as
> E820_TYPE_RAM. This can cause page table entries mapping unaccepted memory
> table to be zapped during phys_pte_init(), phys_pmd_init(), phys_pud_init()
> and phys_p4d_init() as SNP/TDX guest use E820_TYPE_ACPI to store the
> unaccepted memory table and pass it between the kernels on
> kexec/kdump.
> 
> E820_TYPE_ACPI covers not only ACPI data, but also EFI tables and might
> be required by kernel to function properly.
> 
> The problem was discovered during debugging kdump for SNP guest. The
> unaccepted memory table stored with E820_TYPE_ACPI and passed between
> the kernels on kdump was getting zapped as the PMD entry mapping this
> is above the E820_TYPE_RAM range for the reserved crashkernel memory.
> 
> Signed-off-by: Ashish Kalra <ashish.kalra@....com>

Acked-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>

I guess it would be better if I take this patch into my kexec patchset. I
guess I just got lucky not to step onto the issue.

-- 
  Kiryl Shutsemau / Kirill A. Shutemov