Re: [PATCH v2 23/27] KVM: x86/mmu: Assert that correct locks are held for page write-tracking

[Yan Zhao]

Tested-by: Yan Zhao <yan.y.zhao@xxxxxxxxx>

On Fri, Mar 10, 2023 at 04:22:54PM -0800, Sean Christopherson wrote:
> When adding/removing gfns to/from write-tracking, assert that mmu_lock
> is held for write, and that either slots_lock or kvm->srcu is held.
> mmu_lock must be held for write to protect gfn_write_track's refcount,
> and SRCU or slots_lock must be held to protect the memslot itself.
> 
> Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx>
> ---
>  arch/x86/kvm/mmu/page_track.c | 17 +++++++++++------
>  1 file changed, 11 insertions(+), 6 deletions(-)
> 
> diff --git a/arch/x86/kvm/mmu/page_track.c b/arch/x86/kvm/mmu/page_track.c
> index 1993db4578e5..ffcd7ac66f9e 100644
> --- a/arch/x86/kvm/mmu/page_track.c
> +++ b/arch/x86/kvm/mmu/page_track.c
> @@ -12,6 +12,7 @@
>   */
>  #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
>  
> +#include <linux/lockdep.h>
>  #include <linux/kvm_host.h>
>  #include <linux/rculist.h>
>  
> @@ -77,9 +78,6 @@ static void update_gfn_write_track(struct kvm_memory_slot *slot, gfn_t gfn,
>   * add guest page to the tracking pool so that corresponding access on that
>   * page will be intercepted.
>   *
> - * It should be called under the protection both of mmu-lock and kvm->srcu
> - * or kvm->slots_lock.
> - *
>   * @kvm: the guest instance we are interested in.
>   * @slot: the @gfn belongs to.
>   * @gfn: the guest page.
> @@ -87,6 +85,11 @@ static void update_gfn_write_track(struct kvm_memory_slot *slot, gfn_t gfn,
>  void kvm_write_track_add_gfn(struct kvm *kvm, struct kvm_memory_slot *slot,
>  			     gfn_t gfn)
>  {
> +	lockdep_assert_held_write(&kvm->mmu_lock);
> +
> +	lockdep_assert_once(lockdep_is_held(&kvm->slots_lock) ||
> +			    srcu_read_lock_held(&kvm->srcu));
> +
>  	if (WARN_ON(!kvm_page_track_write_tracking_enabled(kvm)))
>  		return;
>  
> @@ -107,9 +110,6 @@ EXPORT_SYMBOL_GPL(kvm_write_track_add_gfn);
>   * remove the guest page from the tracking pool which stops the interception
>   * of corresponding access on that page.
>   *
> - * It should be called under the protection both of mmu-lock and kvm->srcu
> - * or kvm->slots_lock.
> - *
>   * @kvm: the guest instance we are interested in.
>   * @slot: the @gfn belongs to.
>   * @gfn: the guest page.
> @@ -117,6 +117,11 @@ EXPORT_SYMBOL_GPL(kvm_write_track_add_gfn);
>  void kvm_write_track_remove_gfn(struct kvm *kvm,
>  				struct kvm_memory_slot *slot, gfn_t gfn)
>  {
> +	lockdep_assert_held_write(&kvm->mmu_lock);
> +
> +	lockdep_assert_once(lockdep_is_held(&kvm->slots_lock) ||
> +			    srcu_read_lock_held(&kvm->srcu));
> +
>  	if (WARN_ON(!kvm_page_track_write_tracking_enabled(kvm)))
>  		return;
>  
> -- 
> 2.40.0.rc1.284.g88254d51c5-goog
>