KVM: x86/mmu: Try to avoid crashing KVM if a MMU memory cache is empty (53a3f487) · Commits · 戴 / test

Attempt to allocate a new object instead of crashing KVM (and likely the kernel) if a memory cache is unexpectedly empty. Use GFP_ATOMIC for the allocation as the caches are used while holding mmu_lock. The immediate BUG_ON() makes the code unnecessarily explosive and led to confusing minimums being used in the past, e.g. allocating 4 objects where 1 would suffice. Reviewed-by:

Ben Gardon <bgardon@google.com> Signed-off-by:

Sean Christopherson <sean.j.christopherson@intel.com> Message-Id: <20200703023545.8771-6-sean.j.christopherson@intel.com> Signed-off-by:

Paolo Bonzini <pbonzini@redhat.com>

arch/x86/kvm/mmu/mmu.c

+15 −6

Original line number	Diff line number	Diff line
		@@ -1061,6 +1061,15 @@ static void walk_shadow_page_lockless_end(struct kvm_vcpu *vcpu)
		local_irq_enable();
		}

		static inline void mmu_memory_cache_alloc_obj(struct kvm_mmu_memory_cache mc,
		gfp_t gfp_flags)
		{
		if (mc->kmem_cache)
		return kmem_cache_zalloc(mc->kmem_cache, gfp_flags);
		else
		return (void *)__get_free_page(gfp_flags);
		}

		static int mmu_topup_memory_cache(struct kvm_mmu_memory_cache *mc, int min)
		{
		void *obj;
		@@ -1068,10 +1077,7 @@ static int mmu_topup_memory_cache(struct kvm_mmu_memory_cache *mc, int min)
		if (mc->nobjs >= min)
		return 0;
		while (mc->nobjs < ARRAY_SIZE(mc->objects)) {
		if (mc->kmem_cache)
		obj = kmem_cache_zalloc(mc->kmem_cache, GFP_KERNEL_ACCOUNT);
		else
		obj = (void *)__get_free_page(GFP_KERNEL_ACCOUNT);
		obj = mmu_memory_cache_alloc_obj(mc, GFP_KERNEL_ACCOUNT);
		if (!obj)
		return mc->nobjs >= min ? 0 : -ENOMEM;
		mc->objects[mc->nobjs++] = obj;
		@@ -1119,8 +1125,11 @@ static void mmu_memory_cache_alloc(struct kvm_mmu_memory_cache mc)
		{
		void *p;

		BUG_ON(!mc->nobjs);
		if (WARN_ON(!mc->nobjs))
		p = mmu_memory_cache_alloc_obj(mc, GFP_ATOMIC \| __GFP_ACCOUNT);
		else
		p = mc->objects[--mc->nobjs];
		BUG_ON(!p);
		return p;
		}

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