[PATCH 12/24] kvm: x86/kvm: RCU dereference tdp mmu page table links

Ben Gardon
2021-01-12T18:12:50Z

In order to protect TDP MMU PT memory with RCU, ensure that page table
links are properly rcu_derefenced.

Reviewed-by: Peter Feiner <pfeiner@google.com>

Signed-off-by: Ben Gardon <bgardon@google.com>
---
arch/x86/kvm/mmu/tdp_iter.c | 6 +++++-
1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kvm/mmu/tdp_iter.c b/arch/x86/kvm/mmu/tdp_iter.c
index 87b7e16911db..82855613ffa0 100644
--- a/arch/x86/kvm/mmu/tdp_iter.c
+++ b/arch/x86/kvm/mmu/tdp_iter.c
@@ -49,6 +49,8 @@ void tdp_iter_start(struct tdp_iter *iter, u64 *root_pt, int root_level,
*/
u64 *spte_to_child_pt(u64 spte, int level)
{
+ u64 *child_pt;
+
/*
* There's no child entry if this entry isn't present or is a
* last-level entry.
@@ -56,7 +58,9 @@ u64 *spte_to_child_pt(u64 spte, int level)
if (!is_shadow_present_pte(spte) || is_last_spte(spte, level))
return NULL;

- return __va(spte_to_pfn(spte) << PAGE_SHIFT);
+ child_pt = __va(spte_to_pfn(spte) << PAGE_SHIFT);
+
+ return rcu_dereference(child_pt);
}

/*
--
2.30.0.284.gd98b1dd5eaa7-goog