Subject: Re: [PATCH v2 0/5] KVM: arm64: Add support for FEAT_IDST

From: Marc Zyngier <[email-masked]>
Date: Thu, 27 Nov 2025 16:38:34 +0000

On Wed, 26 Nov 2025 15:59:46 +0000,
Marc Zyngier <[email-masked]> wrote:
> 
> FEAT_IDST appeared in ARMv8.4, and allows ID registers to be trapped
> if they are not implemented. This only concerns 3 registers (GMID_EL1,
> CCSIDR2_EL1 and SMIDR_EL1), which are part of features that may not be
> exposed to the guest even if present on the host.
> 
> For these registers, the HW should report them with EC=0x18, even if
> the feature isn't implemented.
> 
> Add support for this feature by handling these registers in a specific
> way and implementing GMID_EL1 support in the process. A very basic
> selftest checks that these registers behave as expected.

Except that said selftest indicates that pKVM doesn't do the right
thing and requires similar rework. I now have some patches to address
it, and will repost the series sometime next week.

	M.

-- 
Without deviation from the norm, progress is not possible.