On Mon, 19 Jul 2021 18:18:02 +0100,
Quentin Perret [off-list ref] wrote:

On Thursday 15 Jul 2021 at 17:31:45 (+0100), Marc Zyngier wrote:

quoted

Make sure we don't issue CMOs when mapping something that
is not a memory address in the S2 page tables.

Signed-off-by: Marc Zyngier <maz@kernel.org>
---
 arch/arm64/kvm/hyp/pgtable.c | 16 ++++++++++------
 1 file changed, 10 insertions(+), 6 deletions(-)

diff --git a/arch/arm64/kvm/hyp/pgtable.c b/arch/arm64/kvm/hyp/pgtable.c
index 05321f4165e3..a5874ebd0354 100644
--- a/arch/arm64/kvm/hyp/pgtable.c
+++ b/arch/arm64/kvm/hyp/pgtable.c

@@ -619,12 +619,16 @@ static int stage2_map_walker_try_leaf(u64 addr, u64 end, u32 level,
 	}
 
 	/* Perform CMOs before installation of the guest stage-2 PTE */
-	if (mm_ops->dcache_clean_inval_poc && stage2_pte_cacheable(pgt, new))
-		mm_ops->dcache_clean_inval_poc(kvm_pte_follow(new, mm_ops),
-						granule);
-
-	if (mm_ops->icache_inval_pou && stage2_pte_executable(new))
-		mm_ops->icache_inval_pou(kvm_pte_follow(new, mm_ops), granule);
+	if (kvm_phys_is_valid(phys)) {
+		if (mm_ops->dcache_clean_inval_poc &&
+		    stage2_pte_cacheable(pgt, new))
+			mm_ops->dcache_clean_inval_poc(kvm_pte_follow(new,
+								      mm_ops),
+						       granule);
+		if (mm_ops->icache_inval_pou && stage2_pte_executable(new))
+			mm_ops->icache_inval_pou(kvm_pte_follow(new, mm_ops),
+						 granule);
+	}

Hrmpf so this makes me realize we have a problem here, not really caused
by your patch though.

Specifically, calling kvm_pgtable_stage2_set_owner() can lead to
overriding valid mappings with invalid mappings, which is effectively an
unmap operation. In this case we should issue CMOs when unmapping a
cacheable page to ensure it is clean to the PoC, like the
kvm_pgtable_stage2_unmap() does.

You only need that if you to have a non-cacheable mapping to the same
page. Otherwise, you will be fine.

For pages that are moved from host-EL1 to EL2, we're good (I don't
think we ever have a non-cachable mapping at EL2). However, once we
start moving pages to guests, we'll need something.

Note that you patch is already an improvement over the current state of
things, because calling stage2_pte_cacheable(pgt, new),
kvm_pte_follow(new, mm_ops) and friends is bogus when 'new' is invalid

Yeah, I had it mentally earmarked as a potential stable candidate. We
may have to do a bit better in the light of the above though.

Thanks,

	M.

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

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