[PATCH 3/3] kvm: mmu: Separate pte generation from set_spte

[Ben Gardon]

Separate the functions for generating leaf page table entries from the
function that inserts them into the paging structure. This refactoring
will facilitate changes to the MMU sychronization model to use atomic
compare / exchanges (which are not guaranteed to succeed) instead of a
monolithic MMU lock.

No functional change expected.

Tested by running kvm-unit-tests on an Intel Haswell machine. This
commit introduced no new failures.

This commit can be viewed in Gerrit at:
	https://linux-review.googlesource.com/c/virt/kvm/kvm/+/2360

Signed-off-by: Ben Gardon <bgardon@xxxxxxxxxx>
Reviewed-by: Peter Shier <pshier@xxxxxxxxxx>
---
 arch/x86/kvm/mmu/mmu.c | 52 +++++++++++++++++++++++++++---------------
 1 file changed, 34 insertions(+), 18 deletions(-)

diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index b81010d0edae1..9239ad5265dc6 100644
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -3000,20 +3000,14 @@ static bool kvm_is_mmio_pfn(kvm_pfn_t pfn)
 #define SET_SPTE_WRITE_PROTECTED_PT	BIT(0)
 #define SET_SPTE_NEED_REMOTE_TLB_FLUSH	BIT(1)
 
-static int set_spte(struct kvm_vcpu *vcpu, u64 *sptep,
-		    unsigned int pte_access, int level,
-		    gfn_t gfn, kvm_pfn_t pfn, bool speculative,
-		    bool can_unsync, bool host_writable)
+static u64 make_spte(struct kvm_vcpu *vcpu, unsigned int pte_access, int level,
+		     gfn_t gfn, kvm_pfn_t pfn, u64 old_spte, bool speculative,
+		     bool can_unsync, bool host_writable, bool ad_disabled,
+		     int *ret)
 {
 	u64 spte = 0;
-	int ret = 0;
-	struct kvm_mmu_page *sp;
-
-	if (set_mmio_spte(vcpu, sptep, gfn, pfn, pte_access))
-		return 0;
 
-	sp = page_header(__pa(sptep));
-	if (sp_ad_disabled(sp))
+	if (ad_disabled)
 		spte |= SPTE_AD_DISABLED_MASK;
 	else if (kvm_vcpu_ad_need_write_protect(vcpu))
 		spte |= SPTE_AD_WRPROT_ONLY_MASK;
@@ -3066,27 +3060,49 @@ static int set_spte(struct kvm_vcpu *vcpu, u64 *sptep,
 		 * is responsibility of mmu_get_page / kvm_sync_page.
 		 * Same reasoning can be applied to dirty page accounting.
 		 */
-		if (!can_unsync && is_writable_pte(*sptep))
-			goto set_pte;
+		if (!can_unsync && is_writable_pte(old_spte))
+			return spte;
 
 		if (mmu_need_write_protect(vcpu, gfn, can_unsync)) {
 			pgprintk("%s: found shadow page for %llx, marking ro\n",
 				 __func__, gfn);
-			ret |= SET_SPTE_WRITE_PROTECTED_PT;
+			*ret |= SET_SPTE_WRITE_PROTECTED_PT;
 			pte_access &= ~ACC_WRITE_MASK;
 			spte &= ~(PT_WRITABLE_MASK | SPTE_MMU_WRITEABLE);
 		}
 	}
 
-	if (pte_access & ACC_WRITE_MASK) {
-		kvm_vcpu_mark_page_dirty(vcpu, gfn);
+	if (pte_access & ACC_WRITE_MASK)
 		spte |= spte_shadow_dirty_mask(spte);
-	}
 
 	if (speculative)
 		spte = mark_spte_for_access_track(spte);
 
-set_pte:
+	return spte;
+}
+
+static int set_spte(struct kvm_vcpu *vcpu, u64 *sptep,
+		    unsigned int pte_access, int level,
+		    gfn_t gfn, kvm_pfn_t pfn, bool speculative,
+		    bool can_unsync, bool host_writable)
+{
+	u64 spte = 0;
+	struct kvm_mmu_page *sp;
+	int ret = 0;
+
+	if (set_mmio_spte(vcpu, sptep, gfn, pfn, pte_access))
+		return 0;
+
+	sp = page_header(__pa(sptep));
+
+	spte = make_spte(vcpu, pte_access, level, gfn, pfn, *sptep, speculative,
+			 can_unsync, host_writable, sp_ad_disabled(sp), &ret);
+	if (!spte)
+		return 0;
+
+	if (spte & PT_WRITABLE_MASK)
+		kvm_vcpu_mark_page_dirty(vcpu, gfn);
+
 	if (mmu_spte_update(sptep, spte))
 		ret |= SET_SPTE_NEED_REMOTE_TLB_FLUSH;
 	return ret;
-- 
2.25.0.341.g760bfbb309-goog