Commit 81d480fd authored by Sean Christopherson's avatar Sean Christopherson Committed by Paolo Bonzini
Browse files

KVM: x86/mmu: Wrap sanity check on number of TDP MMU pages with KVM_PROVE_MMU 



Wrap the TDP MMU page counter in CONFIG_KVM_PROVE_MMU so that the sanity
check is omitted from production builds, and more importantly to remove
the atomic accesses to account pages.  A one-off memory leak in production
is relatively uninteresting, and a WARN_ON won't help mitigate a systemic
issue; it's as much about helping triage memory leaks as it is about
detecting them in the first place, and doesn't magically stop the leaks.
I.e. production environments will be quite sad if a severe KVM bug escapes,
regardless of whether or not KVM WARNs.

Signed-off-by: default avatarSean Christopherson <seanjc@google.com>
Message-ID: <20250315023448.2358456-1-seanjc@google.com>
Signed-off-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
parent 0297cdc1

arch/x86/include/asm/kvm_host.h

+6 −1
Original line number Diff line number Diff line
@@ -1472,8 +1472,13 @@ struct kvm_arch { 
	struct once nx_once;



#ifdef CONFIG_X86_64

	/* The number of TDP MMU pages across all roots. */

#ifdef CONFIG_KVM_PROVE_MMU

	/*

	 * The number of TDP MMU pages across all roots.  Used only to sanity

	 * check that KVM isn't leaking TDP MMU pages.

	 */

	atomic64_t tdp_mmu_pages;

#endif



	/*

	 * List of struct kvm_mmu_pages being used as roots.

arch/x86/kvm/mmu/tdp_mmu.c

+7 −1
Original line number Diff line number Diff line
@@ -40,7 +40,9 @@ void kvm_mmu_uninit_tdp_mmu(struct kvm *kvm) 
	kvm_tdp_mmu_invalidate_roots(kvm, KVM_VALID_ROOTS);

	kvm_tdp_mmu_zap_invalidated_roots(kvm, false);



	WARN_ON(atomic64_read(&kvm->arch.tdp_mmu_pages));

#ifdef CONFIG_KVM_PROVE_MMU

	KVM_MMU_WARN_ON(atomic64_read(&kvm->arch.tdp_mmu_pages));

#endif

	WARN_ON(!list_empty(&kvm->arch.tdp_mmu_roots));



	/*
@@ -325,13 +327,17 @@ static void handle_changed_spte(struct kvm *kvm, int as_id, gfn_t gfn, 
static void tdp_account_mmu_page(struct kvm *kvm, struct kvm_mmu_page *sp)

{

	kvm_account_pgtable_pages((void *)sp->spt, +1);

#ifdef CONFIG_KVM_PROVE_MMU

	atomic64_inc(&kvm->arch.tdp_mmu_pages);

#endif

}



static void tdp_unaccount_mmu_page(struct kvm *kvm, struct kvm_mmu_page *sp)

{

	kvm_account_pgtable_pages((void *)sp->spt, -1);

#ifdef CONFIG_KVM_PROVE_MMU

	atomic64_dec(&kvm->arch.tdp_mmu_pages);

#endif

}



/**