Re: [PATCH] x86/tdx: Fix crash on kexec with CONFIG_EISA

[Maciej W. Rozycki]

On Thu, 22 Aug 2024, Kirill A. Shutemov wrote:

> This issue causes real problems:
> 
> 1. If the kernel is compiled with EISA support, it will attempt to probe
>    EISA by reading 4 bytes from the 0x0FFFD9 address (see eisa_bus_probe()).
>    The kernel treats this read as MMIO and accesses this memory via
>    shared mapping as we do for MMIO.
> 
>    KVM converts memory to shared upon such access.
> 
> 2. The same memory range (0xF0000-0x100000) is scanned to look for the MP
>    table (see mpparse_find_mptable()). However, this is not MMIO and it
>    is accessed via private mapping.
> 
>    This will cause a crash if the memory is not private.
> 
> During normal boot, the kernel scans for SMP information before probing
> for EISA, and it boots fine. However, the memory becomes shared and causes
> issues on kexec when the second kernel attempts to scan for SMP information.

 ISTM that `eisa_bus_probe' has to be updated to `memremap' analogously to 
`mpparse_find_mptable', complementing changes such as commit f7750a795687 
("x86, mpparse, x86/acpi, x86/PCI, x86/dmi, SFI: Use memremap() for RAM 
mappings") or commit 5997efb96756 ("x86/boot: Use memremap() to map the 
MPF and MPC data").  Both just access BIOS memory.

 Can you please try and verify if my proposed change at: 
<https://lore.kernel.org/r/alpine.DEB.2.21.2408242025210.30766@xxxxxxxxxxxxxxxxx> 
has fixed the problem for you?

  Maciej