Re: [PATCH v2 0/4] KVM: arm64: vgic-its: Make the ITS table save reliable

[Marc Zyngier]

On Fri, 21 Aug 2026 07:44:41 +0100,
Fuad Tabba <fuad.tabba@xxxxxxxxx> wrote:
> 
> Hi folks,
> 
> Changes since v1 [1]:
>   - Free the LPI translation cache in vgic_mmio_write_its_baser() too,
>     inside the its_lock section. (Eric)
>   - Reworded patch 1 to name the register the write is to. (Eric)
>   - Rebased onto kvmarm/next.
> 
> Marc pointed out on the v2 ITS series [2] that patch 3 fixed the wrong
> end of the problem: KVM should drop the collections when the guest
> changes the table that described them, rather than validating them at
> save time. He also called that patch's -EINVAL a mistake, since it
> aborts a save userspace has to be able to issue. This series does both,
> following his answers [3] to the two open questions: purge the whole
> list, and skip the offending device rather than fail.
> 
> vgic_mmio_write_its_baser() now frees the cached devices or collections
> whenever the stored register value changes, not only when VALID is
> cleared, and drops the translation cache with them. It tests for a
> change rather than a write because the ITS driver rewrites an unchanged
> GITS_BASER<n> on resume. With that in place the check patch 3 added is
> unreachable, so it is reverted, and vgic_its_save_device_tables() skips
> a device the table can no longer address instead of failing the save.
> 
> compute_next_devid_offset() now calls vgic_its_check_id(), which reads
> guest memory for an indirect table, so the save does 2n reads rather
> than n. It stays linear, as the scan stops at the first
> reachable successor. Patch 1's Fixes: tag names a v4.15 commit, so it
> will be picked up for stable. Drop the tag if that is not wanted.
> 
> Patches 1 and 3 apply to v7.2 unchanged, but patch 2 reverts a commit
> only in kvmarm/next, so the series is based there.
> 
> Tested on QEMU: the new selftest, vgic_irq, vgic_lpi_stress and boots.
> Both cases of the new selftest reset and restore the tables they saved,
> and both fail without the series.
> 
> Based on kvmarm/next (aa8e5dc6a7a2a).

Reviewed-by: Marc Zyngier <maz@xxxxxxxxxx>

	M.

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