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

[Kirill A. Shutemov]

On Mon, Mar 18, 2024 at 07:02:45AM +0000, Ashish Kalra wrote:
> From: Ashish Kalra <ashish.kalra@xxxxxxx>
> 
> 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@xxxxxxx>

Acked-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>

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