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Date:   Thu,  8 Jun 2023 15:05:38 -0700
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Message-ID: <20230608220558.39094-1-ctshao@google.com>
Subject: [PATCH v1 1/3] KVM: arm64: Consistently use free_removed_table() for stage-2
From:   Chun-Tse Shao <ctshao@google.com>
To:     linux-kernel@vger.kernel.org, yuzhao@google.com,
        oliver.upton@linux.dev
Cc:     Chun-Tse Shao <ctshao@google.com>, Marc Zyngier <maz@kernel.org>,
        James Morse <james.morse@arm.com>,
        Suzuki K Poulose <suzuki.poulose@arm.com>,
        Zenghui Yu <yuzenghui@huawei.com>,
        Catalin Marinas <catalin.marinas@arm.com>,
        Will Deacon <will@kernel.org>, Ben Gardon <bgardon@google.com>,
        Gavin Shan <gshan@redhat.com>,
        linux-arm-kernel@lists.infradead.org, kvmarm@lists.linux.dev
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From: Oliver Upton <oliver.upton@linux.dev>

free_removed_table() is essential to the RCU-protected parallel walking
scheme, as behind the scenes the cleanup is deferred until an RCU grace
period. Nonetheless, the stage-2 unmap path calls put_page() directly,
which leads to table memory being freed inline with the table walk.

This is safe for the time being, as the stage-2 unmap walker is called
while holding the write lock. A future change to KVM will further relax
the locking mechanics around the stage-2 page tables to allow lock-free
walkers protected only by RCU. As such, switch to the RCU-safe mechanism
for freeing table memory.

Signed-off-by: Oliver Upton <oliver.upton@linux.dev>
Signed-off-by: Chun-Tse Shao <ctshao@google.com>
---
 arch/arm64/kvm/hyp/pgtable.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/arm64/kvm/hyp/pgtable.c b/arch/arm64/kvm/hyp/pgtable.c
index 5282cb9ca4cf..cc1af0286755 100644
--- a/arch/arm64/kvm/hyp/pgtable.c
+++ b/arch/arm64/kvm/hyp/pgtable.c
@@ -1042,7 +1042,7 @@ static int stage2_unmap_walker(const struct kvm_pgtable_visit_ctx *ctx,
 					       kvm_granule_size(ctx->level));
 
 	if (childp)
-		mm_ops->put_page(childp);
+		mm_ops->free_removed_table(childp, ctx->level);
 
 	return 0;
 }
-- 
2.41.0.162.gfafddb0af9-goog