Re: [PATCH v6 0/7] KVM: arm64: Hide unsupported MPAM from the guest

[Oliver Upton <oliver.upton@linux.dev>]

Hi,

Thanks for respinning this Joey.

On Wed, Oct 30, 2024 at 04:03:10PM +0000, Joey Gouly wrote:
> Hi,
> 
> changes since v5 [1]:
> 	- Removed Kconfig option, the KVM traps shouldn't rely on host kernel support
> 	- Renamed cpus_support_* to system_supports_* since that matches other functions
> 	- Replace static branch arm64_mpam_has_hcr with a normal cpufeature capability
> 	- Add MPAM*_EL2 regs to KVM (undef_access)
> 	- Use constants in the test, instead of hardcoded values
> 	- Added R-b and T-b tags
> 	- Rebased on v6.12-rc5
>
> James wrote:
> 	This series fixes up a long standing bug where MPAM was accidentally exposed
> 	to a guest, but the feature was not otherwise trapped or context switched.
> 	This could result in KVM warning about unexpected traps, and injecting an
> 	undef into the guest contradicting the ID registers.
> 	This would prevent an MPAM aware kernel from booting - fortunately, there
> 	aren't any of those.
> 
> 	Ideally, we'd take the MPAM feature away from the ID registers, but that
> 	would leave existing guests unable to migrate to a newer kernel. Instead,
> 	just ignore that field when it matches the hardware. KVM wasn't going to
> 	expose MPAM anyway. The guest will not see MPAM in the id registers.
> 
> 	This series includes the head.S and KVM changes to enable/disable traps. If
> 	MPAM is neither enabled nor emulated by EL3 firmware, these system register
> 	accesses will trap to EL3.
> 	If your kernel doesn't boot, and the problem bisects here - please update
> 	your firmware. MPAM has been supported by trusted firmware since v1.6 in
> 	2018. (also noted on patch 3).

This is looking pretty good to me, and I'd really like to have it in for
6.13.

Will/Catalin, first 3 patches look OK to you?

-- 
Thanks,
Oliver