2021-11-03 16:19:53

by Sean Christopherson

Subject: [PATCH] KVM: x86/mmu: Properly dereference rcu-protected TDP MMU sptep iterator

Wrap the read of iter->sptep in tdp_mmu_map_handle_target_level() with
rcu_dereference(). Shadow pages in the TDP MMU, and thus their SPTEs,
are protected by rcu.

This fixes a Sparse warning at tdp_mmu.c:900:51:
warning: incorrect type in argument 1 (different address spaces)
expected unsigned long long [usertype] *sptep
got unsigned long long [noderef] [usertype] __rcu *[usertype] sptep

Fixes: 7158bee4b475 ("KVM: MMU: pass kvm_mmu_page struct to make_spte")
Cc: Ben Gardon <[email protected]>
Signed-off-by: Sean Christopherson <[email protected]>
---
arch/x86/kvm/mmu/tdp_mmu.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/kvm/mmu/tdp_mmu.c b/arch/x86/kvm/mmu/tdp_mmu.c
index 7c5dd83e52de..a54c3491af42 100644
--- a/arch/x86/kvm/mmu/tdp_mmu.c
+++ b/arch/x86/kvm/mmu/tdp_mmu.c
@@ -897,7 +897,7 @@ static int tdp_mmu_map_handle_target_level(struct kvm_vcpu *vcpu,
struct kvm_page_fault *fault,
struct tdp_iter *iter)
{
- struct kvm_mmu_page *sp = sptep_to_sp(iter->sptep);
+ struct kvm_mmu_page *sp = sptep_to_sp(rcu_dereference(iter->sptep));
u64 new_spte;
int ret = RET_PF_FIXED;
bool wrprot = false;
--
2.33.1.1089.g2158813163f-goog

2021-11-03 16:39:10

by Ben Gardon

Subject: Re: [PATCH] KVM: x86/mmu: Properly dereference rcu-protected TDP MMU sptep iterator

On Wed, Nov 3, 2021 at 9:18 AM Sean Christopherson <[email protected]> wrote:
>
> Wrap the read of iter->sptep in tdp_mmu_map_handle_target_level() with
> rcu_dereference(). Shadow pages in the TDP MMU, and thus their SPTEs,
> are protected by rcu.
>
> This fixes a Sparse warning at tdp_mmu.c:900:51:
> warning: incorrect type in argument 1 (different address spaces)
> expected unsigned long long [usertype] *sptep
> got unsigned long long [noderef] [usertype] __rcu *[usertype] sptep
>
> Fixes: 7158bee4b475 ("KVM: MMU: pass kvm_mmu_page struct to make_spte")
> Cc: Ben Gardon <[email protected]>
> Signed-off-by: Sean Christopherson <[email protected]>

Reviewed-by: Ben Gardon <[email protected]>

This change looks good to me. It also reminds me that the struct
kvm_mmu_pages are also protected by RCU.
I wonder if it would be worth creating something similar to tdp_ptep_t
for the struct kvm_mmu_pages to add RCU annotations to them as well.

> ---
> arch/x86/kvm/mmu/tdp_mmu.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/arch/x86/kvm/mmu/tdp_mmu.c b/arch/x86/kvm/mmu/tdp_mmu.c
> index 7c5dd83e52de..a54c3491af42 100644
> --- a/arch/x86/kvm/mmu/tdp_mmu.c
> +++ b/arch/x86/kvm/mmu/tdp_mmu.c
> @@ -897,7 +897,7 @@ static int tdp_mmu_map_handle_target_level(struct kvm_vcpu *vcpu,
> struct kvm_page_fault *fault,
> struct tdp_iter *iter)
> {
> - struct kvm_mmu_page *sp = sptep_to_sp(iter->sptep);
> + struct kvm_mmu_page *sp = sptep_to_sp(rcu_dereference(iter->sptep));
> u64 new_spte;
> int ret = RET_PF_FIXED;
> bool wrprot = false;
> --
> 2.33.1.1089.g2158813163f-goog
>