linux-kernel - [PATCH mm-unstable v2 06/10] kvm/powerpc: make radix page tables RCU safe

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Date:   Fri, 26 May 2023 17:44:31 -0600
From:   Yu Zhao <yuzhao@...gle.com>
To:     Andrew Morton <akpm@...ux-foundation.org>,
        Paolo Bonzini <pbonzini@...hat.com>
Cc:     Alistair Popple <apopple@...dia.com>,
        Anup Patel <anup@...infault.org>,
        Ben Gardon <bgardon@...gle.com>,
        Borislav Petkov <bp@...en8.de>,
        Catalin Marinas <catalin.marinas@....com>,
        Chao Peng <chao.p.peng@...ux.intel.com>,
        Christophe Leroy <christophe.leroy@...roup.eu>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Fabiano Rosas <farosas@...ux.ibm.com>,
        Gaosheng Cui <cuigaosheng1@...wei.com>,
        Gavin Shan <gshan@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...hat.com>,
        James Morse <james.morse@....com>,
        "Jason A. Donenfeld" <Jason@...c4.com>,
        Jason Gunthorpe <jgg@...pe.ca>,
        Jonathan Corbet <corbet@....net>,
        Marc Zyngier <maz@...nel.org>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        Michael Larabel <michael@...haellarabel.com>,
        Mike Rapoport <rppt@...nel.org>,
        Nicholas Piggin <npiggin@...il.com>,
        Oliver Upton <oliver.upton@...ux.dev>,
        Paul Mackerras <paulus@...abs.org>,
        Peter Xu <peterx@...hat.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Suzuki K Poulose <suzuki.poulose@....com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Thomas Huth <thuth@...hat.com>, Will Deacon <will@...nel.org>,
        Zenghui Yu <yuzenghui@...wei.com>, kvmarm@...ts.linux.dev,
        kvm@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, linuxppc-dev@...ts.ozlabs.org,
        linux-trace-kernel@...r.kernel.org, x86@...nel.org,
        linux-mm@...gle.com, Yu Zhao <yuzhao@...gle.com>
Subject: [PATCH mm-unstable v2 06/10] kvm/powerpc: make radix page tables RCU safe

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@...gle.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