[PATCH v2 1/4] KVM: arm64: vgic-its: Free the caches when GITS_BASER changes

[Fuad Tabba <fuad.tabba@linux.dev>]

A guest that disables the ITS and re-points or shrinks GITS_BASER<n>
with VALID still set keeps the devices and collections it mapped
against the old table, as KVM frees them only when VALID is cleared.
The contents of the table are IMPLEMENTATION DEFINED, so a write that
gives GITS_BASER<n> a different address or size may lose whatever the
old value described. Free the list whenever the stored value changes,
and drop the translation cache with it.

The cache is not empty just because the ITS is disabled: its->enabled
is written under the cmd_lock, while vgic_its_resolve_lpi() tests it
under the its_lock, so an injection can still cache an entry after the
ITS was disabled. Hence the invalidation inside the its_lock section.

Test for a change rather than a write: its_restore_enable() rewrites
GITS_BASER<n> from its probe-time cache on resume, and KVM reports
GITS_TYPER.HCC as 0, so nothing re-maps the boot CPU's collection
afterwards.

Fixes: 36d6961c2b481 ("KVM: arm/arm64: vgic-its: Free caches when GITS_BASER Valid bit is cleared")
Suggested-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/all/87ecg9owwa.wl-maz@kernel.org/
Signed-off-by: Fuad Tabba <fuad.tabba@linux.dev>
---
 arch/arm64/kvm/vgic/vgic-its.c | 11 ++++++++---
 1 file changed, 8 insertions(+), 3 deletions(-)

diff --git a/arch/arm64/kvm/vgic/vgic-its.c b/arch/arm64/kvm/vgic/vgic-its.c
index f6538b1976f9b..d5ede640812c4 100644
--- a/arch/arm64/kvm/vgic/vgic-its.c
+++ b/arch/arm64/kvm/vgic/vgic-its.c
@@ -1649,7 +1649,7 @@ static void vgic_mmio_write_its_baser(struct kvm *kvm,
 				      unsigned long val)
 {
 	const struct vgic_its_abi *abi = vgic_its_get_abi(its);
-	u64 entry_size, table_type;
+	u64 old, entry_size, table_type;
 	u64 reg, *regptr, clearbits = 0;
 
 	/* When GITS_CTLR.Enable is 1, we ignore write accesses. */
@@ -1672,7 +1672,9 @@ static void vgic_mmio_write_its_baser(struct kvm *kvm,
 		return;
 	}
 
-	reg = update_64bit_reg(*regptr, addr & 7, len, val);
+	old = *regptr;
+
+	reg = update_64bit_reg(old, addr & 7, len, val);
 	reg &= ~GITS_BASER_RO_MASK;
 	reg &= ~clearbits;
 
@@ -1682,7 +1684,8 @@ static void vgic_mmio_write_its_baser(struct kvm *kvm,
 
 	*regptr = reg;
 
-	if (!(reg & GITS_BASER_VALID)) {
+	/* The ITS driver rewrites an unchanged GITS_BASER<n> on resume. */
+	if (reg != old) {
 		/* Take the its_lock to prevent a race with a save/restore */
 		mutex_lock(&its->its_lock);
 		switch (table_type) {
@@ -1693,6 +1696,8 @@ static void vgic_mmio_write_its_baser(struct kvm *kvm,
 			vgic_its_free_collection_list(kvm, its);
 			break;
 		}
+		/* A concurrent injection may have cached a translation. */
+		vgic_its_invalidate_cache(its);
 		mutex_unlock(&its->its_lock);
 	}
 }
-- 
2.39.5