linux-kernel - Re: [PATCH] x86/tdx: Fix crash on kexec with CONFIG

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Message-ID: <alpine.DEB.2.21.2408240952080.30766@angie.orcam.me.uk>
Date: Sat, 24 Aug 2024 23:29:39 +0100 (BST)
From: "Maciej W. Rozycki" <macro@...am.me.uk>
To: "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
cc: Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>, 
    Borislav Petkov <bp@...en8.de>, Dave Hansen <dave.hansen@...ux.intel.com>, 
    x86@...nel.org, "H. Peter Anvin" <hpa@...or.com>, 
    Kevin Loughlin <kevinloughlin@...gle.com>, linux-kernel@...r.kernel.org, 
    Rick Edgecombe <rick.p.edgecombe@...el.com>, 
    Isaku Yamahata <isaku.yamahata@...el.com>
Subject: Re: [PATCH] x86/tdx: Fix crash on kexec with CONFIG_EISA

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@angie.orcam.me.uk> 
has fixed the problem for you?

  Maciej