linux-kernel - [Patch v2 1/5] KVM: x86/mmu: Make separate function to check for SPTEs atomic write conditions

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Date:   Fri,  3 Feb 2023 11:28:18 -0800
From:   Vipin Sharma <vipinsh@...gle.com>
To:     seanjc@...gle.com, pbonzini@...hat.com, bgardon@...gle.com,
        dmatlack@...gle.com
Cc:     kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        Vipin Sharma <vipinsh@...gle.com>
Subject: [Patch v2 1/5] KVM: x86/mmu: Make separate function to check for
 SPTEs atomic write conditions

Move condition checks in kvm_tdp_mmu_write_spte() for writing spte
atomically in a separate function.

New function will be used in future commits to clear bits in SPTE.

Signed-off-by: Vipin Sharma <vipinsh@...gle.com>
---
 arch/x86/kvm/mmu/tdp_iter.h | 16 +++++++++++-----
 1 file changed, 11 insertions(+), 5 deletions(-)

diff --git a/arch/x86/kvm/mmu/tdp_iter.h b/arch/x86/kvm/mmu/tdp_iter.h
index f0af385c56e0..30a52e5e68de 100644
--- a/arch/x86/kvm/mmu/tdp_iter.h
+++ b/arch/x86/kvm/mmu/tdp_iter.h
@@ -29,11 +29,10 @@ static inline void __kvm_tdp_mmu_write_spte(tdp_ptep_t sptep, u64 new_spte)
 	WRITE_ONCE(*rcu_dereference(sptep), new_spte);
 }
 
-static inline u64 kvm_tdp_mmu_write_spte(tdp_ptep_t sptep, u64 old_spte,
-					 u64 new_spte, int level)
+static inline bool kvm_tdp_mmu_spte_has_volatile_bits(u64 old_spte, int level)
 {
 	/*
-	 * Atomically write the SPTE if it is a shadow-present, leaf SPTE with
+	 * Atomically write SPTEs if it is a shadow-present, leaf SPTE with
 	 * volatile bits, i.e. has bits that can be set outside of mmu_lock.
 	 * The Writable bit can be set by KVM's fast page fault handler, and
 	 * Accessed and Dirty bits can be set by the CPU.
@@ -44,8 +43,15 @@ static inline u64 kvm_tdp_mmu_write_spte(tdp_ptep_t sptep, u64 old_spte,
 	 * logic needs to be reassessed if KVM were to use non-leaf Accessed
 	 * bits, e.g. to skip stepping down into child SPTEs when aging SPTEs.
 	 */
-	if (is_shadow_present_pte(old_spte) && is_last_spte(old_spte, level) &&
-	    spte_has_volatile_bits(old_spte))
+	return is_shadow_present_pte(old_spte) &&
+	       is_last_spte(old_spte, level) &&
+	       spte_has_volatile_bits(old_spte);
+}
+
+static inline u64 kvm_tdp_mmu_write_spte(tdp_ptep_t sptep, u64 old_spte,
+					 u64 new_spte, int level)
+{
+	if (kvm_tdp_mmu_spte_has_volatile_bits(old_spte, level))
 		return kvm_tdp_mmu_write_spte_atomic(sptep, new_spte);
 
 	__kvm_tdp_mmu_write_spte(sptep, new_spte);
-- 
2.39.1.519.gcb327c4b5f-goog