2023-07-29 01:19:00

by Sean Christopherson

Subject: [PATCH v3 09/12] KVM: x86/mmu: Replace MMU_DEBUG with proper KVM_PROVE_MMU Kconfig

Replace MMU_DEBUG, which requires manually modifying KVM to enable the
macro, with a proper Kconfig, KVM_PROVE_MMU. Now that pgprintk() and
rmap_printk() are gone, i.e. the macro guards only KVM_MMU_WARN_ON() and
won't flood the kernel logs, enabling the option for debug kernels is both
desirable and feasible.

Signed-off-by: Sean Christopherson <[email protected]>
---
arch/x86/kvm/Kconfig | 13 +++++++++++++
arch/x86/kvm/mmu/mmu.c | 2 +-
arch/x86/kvm/mmu/mmu_internal.h | 4 +---
3 files changed, 15 insertions(+), 4 deletions(-)

diff --git a/arch/x86/kvm/Kconfig b/arch/x86/kvm/Kconfig
index 89ca7f4c1464..4e5a282cc518 100644
--- a/arch/x86/kvm/Kconfig
+++ b/arch/x86/kvm/Kconfig
@@ -138,6 +138,19 @@ config KVM_XEN

If in doubt, say "N".

+config KVM_PROVE_MMU
+ bool "Prove KVM MMU correctness"
+ depends on DEBUG_KERNEL
+ depends on KVM
+ depends on EXPERT
+ help
+ Enables runtime assertions in KVM's MMU that are too costly to enable
+ in anything remotely resembling a production environment, e.g. this
+ gates code that verifies a to-be-freed page table doesn't have any
+ present SPTEs.
+
+ If in doubt, say "N".
+
config KVM_EXTERNAL_WRITE_TRACKING
bool

diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index d46f77734f30..21ced900c3e9 100644
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -1695,7 +1695,7 @@ bool kvm_test_age_gfn(struct kvm *kvm, struct kvm_gfn_range *range)

static void kvm_mmu_check_sptes_at_free(struct kvm_mmu_page *sp)
{
-#ifdef MMU_DEBUG
+#ifdef CONFIG_KVM_PROVE_MMU
int i;

for (i = 0; i < SPTE_ENT_PER_PAGE; i++) {
diff --git a/arch/x86/kvm/mmu/mmu_internal.h b/arch/x86/kvm/mmu/mmu_internal.h
index cfe925fefa68..40e74db6a7d5 100644
--- a/arch/x86/kvm/mmu/mmu_internal.h
+++ b/arch/x86/kvm/mmu/mmu_internal.h
@@ -6,9 +6,7 @@
#include <linux/kvm_host.h>
#include <asm/kvm_host.h>

-#undef MMU_DEBUG
-
-#ifdef MMU_DEBUG
+#ifdef CONFIG_KVM_PROVE_MMU
#define KVM_MMU_WARN_ON(x) WARN_ON_ONCE(x)
#else
#define KVM_MMU_WARN_ON(x) do { } while (0)
--
2.41.0.487.g6d72f3e995-goog

2023-08-01 15:23:43

by Philippe Mathieu-Daudé

Subject: Re: [PATCH v3 09/12] KVM: x86/mmu: Replace MMU_DEBUG with proper KVM_PROVE_MMU Kconfig

On 29/7/23 02:47, Sean Christopherson wrote:
> Replace MMU_DEBUG, which requires manually modifying KVM to enable the
> macro, with a proper Kconfig, KVM_PROVE_MMU. Now that pgprintk() and
> rmap_printk() are gone, i.e. the macro guards only KVM_MMU_WARN_ON() and
> won't flood the kernel logs, enabling the option for debug kernels is both
> desirable and feasible.
>
> Signed-off-by: Sean Christopherson <[email protected]>
> ---
> arch/x86/kvm/Kconfig | 13 +++++++++++++
> arch/x86/kvm/mmu/mmu.c | 2 +-
> arch/x86/kvm/mmu/mmu_internal.h | 4 +---
> 3 files changed, 15 insertions(+), 4 deletions(-)

Reviewed-by: Philippe Mathieu-Daudé <[email protected]>