Re: [PATCH] x86/unaccepted_memory: Do not accept ranges that are no longer E820 RAM

[Ard Biesheuvel]

Hello Pankaj,

On Mon, 2 Nov 2026, at 12:31, Pankaj Gupta wrote:
> The EFI stub builds the unaccepted memory bitmap before the kernel parses
> its command line.  Option memmap=<size>$<addr> removes RAM from the E820
> map while its bits are still set in the bitmap.
>
> The removed range, such as a memmap=...$... hole, is then still treated as
> unaccepted RAM and accept_memory() tries to accept it.  The hole is not
> mapped, so on SEV-SNP the PVALIDATE faults and the guest crashes early in
> the boot:
>
>   BUG: unable to handle page fault for address: ffff8a14bfe00000
>   RIP: 0010:pvalidate_pages+0xc0/0x250
>    set_pages_state+0x41a/0x440
>    snp_accept_memory+0x3e/0x50
>    accept_memory+0x186/0x260
>    __free_pages_core+0xd2/0x240
>    memblock_free_pages+0x1b/0x30
>    memblock_free_all+0x275/0x2d0
>
> This was seen with memmap=2M$0x1ffe00000, a 2 MiB hole in RAM, on a 19 GiB
> SNP guest with lazy acceptance.
>
> Fixes: 2053bc57f367 ("efi: Add unaccepted memory support")
> Signed-off-by: Pankaj Gupta <pankaj.gupta@xxxxxxx>
> ---
>  arch/x86/include/asm/unaccepted_memory.h | 23 ++++++++++++++++++++++-
>  1 file changed, 22 insertions(+), 1 deletion(-)
>

Can we just disallow memmap= when running in a confidential VM?