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Date:   Fri, 26 May 2023 17:44:31 -0600
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Subject: [PATCH mm-unstable v2 06/10] kvm/powerpc: make radix page tables RCU safe
From:   Yu Zhao <yuzhao@google.com>
To:     Andrew Morton <akpm@linux-foundation.org>,
        Paolo Bonzini <pbonzini@redhat.com>
Cc:     Alistair Popple <apopple@nvidia.com>,
        Anup Patel <anup@brainfault.org>,
        Ben Gardon <bgardon@google.com>,
        Borislav Petkov <bp@alien8.de>,
        Catalin Marinas <catalin.marinas@arm.com>,
        Chao Peng <chao.p.peng@linux.intel.com>,
        Christophe Leroy <christophe.leroy@csgroup.eu>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        Fabiano Rosas <farosas@linux.ibm.com>,
        Gaosheng Cui <cuigaosheng1@huawei.com>,
        Gavin Shan <gshan@redhat.com>,
        "H. Peter Anvin" <hpa@zytor.com>, Ingo Molnar <mingo@redhat.com>,
        James Morse <james.morse@arm.com>,
        "Jason A. Donenfeld" <Jason@zx2c4.com>,
        Jason Gunthorpe <jgg@ziepe.ca>,
        Jonathan Corbet <corbet@lwn.net>,
        Marc Zyngier <maz@kernel.org>,
        Masami Hiramatsu <mhiramat@kernel.org>,
        Michael Ellerman <mpe@ellerman.id.au>,
        Michael Larabel <michael@michaellarabel.com>,
        Mike Rapoport <rppt@kernel.org>,
        Nicholas Piggin <npiggin@gmail.com>,
        Oliver Upton <oliver.upton@linux.dev>,
        Paul Mackerras <paulus@ozlabs.org>,
        Peter Xu <peterx@redhat.com>,
        Sean Christopherson <seanjc@google.com>,
        Steven Rostedt <rostedt@goodmis.org>,
        Suzuki K Poulose <suzuki.poulose@arm.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Thomas Huth <thuth@redhat.com>, Will Deacon <will@kernel.org>,
        Zenghui Yu <yuzenghui@huawei.com>, kvmarm@lists.linux.dev,
        kvm@vger.kernel.org, linux-arm-kernel@lists.infradead.org,
        linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org,
        linux-mm@kvack.org, linuxppc-dev@lists.ozlabs.org,
        linux-trace-kernel@vger.kernel.org, x86@kernel.org,
        linux-mm@google.com, Yu Zhao <yuzhao@google.com>
Content-Type: text/plain; charset="UTF-8"
Precedence: bulk

KVM page tables are currently not RCU safe against remapping, i.e.,
kvmppc_unmap_free_pmd_entry_table() et al. The previous
mmu_notifier_ops members rely on kvm->mmu_lock to synchronize with
that operation.

However, the new mmu_notifier_ops member test_clear_young() provides
a fast path that does not take kvm->mmu_lock. To implement
kvm_arch_test_clear_young() for that path, orphan page tables need to
be freed by RCU.

Unmapping, specifically kvm_unmap_radix(), does not free page tables,
hence not a concern.

Signed-off-by: Yu Zhao <yuzhao@google.com>
---
 arch/powerpc/kvm/book3s_64_mmu_radix.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/arch/powerpc/kvm/book3s_64_mmu_radix.c b/arch/powerpc/kvm/book3s_64_mmu_radix.c
index 461307b89c3a..3b65b3b11041 100644
--- a/arch/powerpc/kvm/book3s_64_mmu_radix.c
+++ b/arch/powerpc/kvm/book3s_64_mmu_radix.c
@@ -1469,13 +1469,15 @@ int kvmppc_radix_init(void)
 {
 	unsigned long size = sizeof(void *) << RADIX_PTE_INDEX_SIZE;
 
-	kvm_pte_cache = kmem_cache_create("kvm-pte", size, size, 0, pte_ctor);
+	kvm_pte_cache = kmem_cache_create("kvm-pte", size, size,
+					  SLAB_TYPESAFE_BY_RCU, pte_ctor);
 	if (!kvm_pte_cache)
 		return -ENOMEM;
 
 	size = sizeof(void *) << RADIX_PMD_INDEX_SIZE;
 
-	kvm_pmd_cache = kmem_cache_create("kvm-pmd", size, size, 0, pmd_ctor);
+	kvm_pmd_cache = kmem_cache_create("kvm-pmd", size, size,
+					  SLAB_TYPESAFE_BY_RCU, pmd_ctor);
 	if (!kvm_pmd_cache) {
 		kmem_cache_destroy(kvm_pte_cache);
 		return -ENOMEM;
-- 
2.41.0.rc0.172.g3f132b7071-goog