Re: [PATCH v10 0/4] x86/pvh: fix unbootable VMs again (PVH + KASAN)

[Borislav Petkov]

On Mon, Sep 21, 2026 at 10:36:31PM -0300, Mauricio Faria de Oliveira wrote:
> The issue of unbootable VMs with CONFIG_PVH due to CONFIG_KASAN is back.
> 
> Booting directly from vmlinux (instead of bzImage) now fails with gcc-14/15
> (but works with gcc-12/13) if CONFIG_KASAN_GENERIC is set, on Ubuntu 25.10.
> 
> The PVH code is required/supposed not to use the KASAN memory access check
> in the kernel entry point as KASAN has not yet been setup, or an exception
> is hit and the boot fails.
> 
> This was previously described and addressed with __builtin_mem{cmp,set}():
> - commit 661362e3dcab ("xen, pvh: fix unbootable VMs (PVH + KASAN - AMD_MEM_ENCRYPT)")
> - commit 416a33c9afce ("x86/cpu: fix unbootable VMs by inlining memcmp() in hypervisor_cpuid_base()")
> - commit fbe5a6dfe492 ("xen, pvh: fix unbootable VMs by inlining memset() in xen_prepare_pvh()")
> 
> However, even with __builtin the compiler may decide to use the out of line
> function instead of the inline implementation. So, that does not really fix
> the issue unconditionally; see details below.

So, this whole deal doesn't sound to me like we need to backport it to stable
- it rather looks more like fixing some configs which want to enable KASAN on
PVH guests.

In that case, I'll queue this for 7.4.

If this needs to go to stable, then there better be a pretty good reason for
it.

Right?

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette