On Mon, Nov 28, 2022 at 06:52:22PM +0000, Vincent Donnefort wrote:
> From: Marc Zyngier <maz@xxxxxxxxxx>
>
> The kernel has an awfully complicated boot sequence in order to cope
> with the various EL2 configurations, including those that "enhanced"
> the architecture. We go from EL2 to EL1, then back to EL2, staying
> at EL2 if VHE capable and otherwise go back to EL1.
>
> Here's a paracetamol tablet for you.
>
> The cpu_resume path follows the same logic, because coming up with
> two versions of a square wheel is hard.
>
> However, things aren't this straightforward with pKVM, as the host
> resume path is always proxied by the hypervisor, which means that
> the kernel is always entered at EL1. Which contradicts what the
> __boot_cpu_mode[] array contains (it obviously says EL2).
>
> This thus triggers a HVC call from EL1 to EL2 in a vain attempt
> to upgrade from EL1 to EL2 VHE, which we are, funnily enough,
> reluctant to grant to the host kernel. This is also completely
> unexpected, and puzzles your average EL2 hacker.
>
> Address it by fixing up the boot mode at the point the host gets
> deprivileged. is_hyp_mode_available() and co already have a static
> branch to deal with this, making it pretty safe.
>
> This stable fix doesn't have an upstream version. The entire bootflow
> has been reworked from 6.0 and that fixed the boot mode at the same
> time, from commit 005e12676af0 ("arm64: head: record CPU boot mode after
> enabling the MMU") to be precise. However, the latter is part of a 20
> patches long series and can't be simply cherry-pick'ed.
>
> Link: https://lore.kernel.org/r/20220624150651.1358849-1-ardb@xxxxxxxxxx/
> Link: https://lore.kernel.org/r/20221011165400.1241729-1-maz@xxxxxxxxxx/
> Cc: <stable@xxxxxxxxxxxxxxx> # 5.15+
> Reported-by: Vincent Donnefort <vdonnefort@xxxxxxxxxx>
> Signed-off-by: Marc Zyngier <maz@xxxxxxxxxx>
> Tested-by: Vincent Donnefort <vdonnefort@xxxxxxxxxx>
> [Vincent: Add a paragraph about why this patch is for stable only]
> Signed-off-by: Vincent Donnefort <vdonnefort@xxxxxxxxxx>
Now queued up, thanks.
greg k-h
