Re: [PATCH v2 0/2] x86/sev-es: Resolve early #VC handler UB

[Ingo Molnar]

* Adam Dunlap <acdunlap@xxxxxxxxxx> wrote:

> In v0 of this patch, I mistakenly claimed that
> boot_cpu_data.x86_virt_bits was not getting set to 0 in some
> configurations. However, it is in fact reliably being set to 0 because
> it is specified to be in the .data..read_mostly section, and .data is
> initialized at this point. The boot failures that we were seeing were
> actually due to the gcc 12.3 compiler exploiting the undefined
> behavior to return false from __is_canonical_address when
> boot_cpu_data.x86_virt_bits is 0.
> 
> This patch set applies the 2 changes posted by Dave Hansen: remove the
> UB by explicily checking for 0, and remove the period of time where
> x86_virt_bits may be temporarily set to the wrong value where the #VC
> handler could observe it.
> 
> 
> Adam Dunlap (2):
>   x86/sev-es: Allow copy_from_kernel_nofault in earlier boot
>   x86/sev-es: Only set x86_virt_bits to correct value

I've applied these fixes to tip:x86/mm, thanks!

Note that I switched around the order of patches: we first want
to enhance x86_virt_bits to be reliable, only then do we want to
change copy_from_kernel_nofault_allowed() to be able to rely on it,
to fix early #VC accesses, right?

I also improved the changelogs & titles a bit.

Thanks,

	Ingo