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From: "Maciej S. Szmigiero" <mail@maciej.szmigiero.name>
To: Paolo Bonzini <pbonzini@redhat.com>
Cc: Sean Christopherson <seanjc@google.com>,
	Vitaly Kuznetsov <vkuznets@redhat.com>,
	Wanpeng Li <wanpengli@tencent.com>,
	Jim Mattson <jmattson@google.com>, Joerg Roedel <joro@8bytes.org>,
	Igor Mammedov <imammedo@redhat.com>,
	kvm@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: [PATCH 1/3] KVM: x86: Avoid overflowing nr_mmu_pages in kvm_arch_commit_memory_region()
Date: Fri, 26 Nov 2021 01:31:07 +0100	[thread overview]
Message-ID: <44edcde46d12c2f5376a1cd1429650acb506ebaf.1637884349.git.maciej.szmigiero@oracle.com> (raw)
In-Reply-To: <cover.1637884349.git.maciej.szmigiero@oracle.com>

From: "Maciej S. Szmigiero" <maciej.szmigiero@oracle.com>

With kvm->nr_memslot_pages capped at ULONG_MAX we can't safely multiply it
by KVM_PERMILLE_MMU_PAGES (20) since this operation can possibly overflow
an unsigned long variable.

Rewrite this "* 20 / 1000" operation as "/ 50" instead to avoid such
overflow.

Signed-off-by: Maciej S. Szmigiero <maciej.szmigiero@oracle.com>
---
 arch/x86/include/asm/kvm_host.h | 2 +-
 arch/x86/kvm/x86.c              | 3 +--
 2 files changed, 2 insertions(+), 3 deletions(-)

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index 1fcb345bc107..8cd1d254c948 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -135,7 +135,7 @@
 #define KVM_HPAGE_MASK(x)	(~(KVM_HPAGE_SIZE(x) - 1))
 #define KVM_PAGES_PER_HPAGE(x)	(KVM_HPAGE_SIZE(x) / PAGE_SIZE)
 
-#define KVM_PERMILLE_MMU_PAGES 20
+#define KVM_MEMSLOT_PAGES_TO_MMU_PAGES_RATIO 50
 #define KVM_MIN_ALLOC_MMU_PAGES 64UL
 #define KVM_MMU_HASH_SHIFT 12
 #define KVM_NUM_MMU_PAGES (1 << KVM_MMU_HASH_SHIFT)
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 04e8dabc187d..69330b395f12 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -11753,8 +11753,7 @@ void kvm_arch_commit_memory_region(struct kvm *kvm,
 	    (change == KVM_MR_CREATE || change == KVM_MR_DELETE)) {
 		unsigned long nr_mmu_pages;
 
-		nr_mmu_pages = kvm->nr_memslot_pages * KVM_PERMILLE_MMU_PAGES;
-		nr_mmu_pages /= 1000;
+		nr_mmu_pages = kvm->nr_memslot_pages / KVM_MEMSLOT_PAGES_TO_MMU_PAGES_RATIO;
 		nr_mmu_pages = max(nr_mmu_pages, KVM_MIN_ALLOC_MMU_PAGES);
 		kvm_mmu_change_mmu_pages(kvm, nr_mmu_pages);
 	}

  reply	other threads:[~2021-11-26  0:33 UTC|newest]

Thread overview: 9+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-11-26  0:31 [PATCH 0/3] KVM: Scalable memslots implementation additional patches Maciej S. Szmigiero
2021-11-26  0:31 ` Maciej S. Szmigiero [this message]
2021-11-29 21:03   ` [PATCH 1/3] KVM: x86: Avoid overflowing nr_mmu_pages in kvm_arch_commit_memory_region() Sean Christopherson
2021-11-26  0:31 ` [PATCH 2/3] KVM: Use atomic_long_cmpxchg() instead of an open-coded variant Maciej S. Szmigiero
2021-11-26 10:34   ` Paolo Bonzini
2021-11-26  0:31 ` [PATCH 3/3] KVM: Make kvm_for_each_memslot_in_gfn_range() strict and use iterators Maciej S. Szmigiero
2021-11-26 10:35 ` [PATCH 0/3] KVM: Scalable memslots implementation additional patches Paolo Bonzini
2021-11-26 13:18   ` Maciej S. Szmigiero
2021-11-26 13:19     ` Paolo Bonzini

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