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

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Date:   Tue, 12 Jan 2021 10:10:29 -0800
From:   Ben Gardon <bgardon@...gle.com>
To:     linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Cc:     Paolo Bonzini <pbonzini@...hat.com>, Peter Xu <peterx@...hat.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Peter Shier <pshier@...gle.com>,
        Peter Feiner <pfeiner@...gle.com>,
        Junaid Shahid <junaids@...gle.com>,
        Jim Mattson <jmattson@...gle.com>,
        Yulei Zhang <yulei.kernel@...il.com>,
        Wanpeng Li <kernellwp@...il.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Xiao Guangrong <xiaoguangrong.eric@...il.com>,
        Ben Gardon <bgardon@...gle.com>
Subject: [PATCH 12/24] kvm: x86/kvm: RCU dereference tdp mmu page table links

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

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

Signed-off-by: Ben Gardon <bgardon@...gle.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