Re: [PATCH 6/5] KVM: MMU: Optimize is_last_gpte()

[Avi Kivity <avi@redhat.com>]

On 09/12/2012 09:03 PM, Avi Kivity wrote:
> On 09/12/2012 08:49 PM, Avi Kivity wrote:
>> Instead of branchy code depending on level, gpte.ps, and mmu configuration,
>> prepare everything in a bitmap during mode changes and look it up during
>> runtime.
> 
> 6/5 is buggy, sorry, will update it tomorrow.
> 
> 

--------8<----------8<--------------

From: Avi Kivity <avi@redhat.com>
Date: Wed, 12 Sep 2012 20:46:56 +0300
Subject: [PATCH v2 6/5] KVM: MMU: Optimize is_last_gpte()

Instead of branchy code depending on level, gpte.ps, and mmu configuration,
prepare everything in a bitmap during mode changes and look it up during
runtime.

Signed-off-by: Avi Kivity <avi@redhat.com>
---

v2: rearrange bitmap (one less shift)
    avoid stomping on local variable
    fix index calculation
    move check back to a function

 arch/x86/include/asm/kvm_host.h |  7 +++++++
 arch/x86/kvm/mmu.c              | 31 +++++++++++++++++++++++++++++++
 arch/x86/kvm/mmu.h              |  3 ++-
 arch/x86/kvm/paging_tmpl.h      | 22 +---------------------
 4 files changed, 41 insertions(+), 22 deletions(-)

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index 3318bde..f9a48cf 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -298,6 +298,13 @@ struct kvm_mmu {
 	u64 *lm_root;
 	u64 rsvd_bits_mask[2][4];
 
+	/*
+	 * Bitmap: bit set = last pte in walk
+	 * index[0]: pte.ps
+	 * index[1:2]: level
+	 */
+	u8 last_pte_bitmap;
+
 	bool nx;
 
 	u64 pdptrs[4]; /* pae */
diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
index ce78408..32fe597 100644
--- a/arch/x86/kvm/mmu.c
+++ b/arch/x86/kvm/mmu.c
@@ -3447,6 +3447,15 @@ static inline unsigned gpte_access(struct kvm_vcpu *vcpu, u64 gpte)
 	return access;
 }
 
+static inline bool is_last_gpte(struct kvm_mmu *mmu, unsigned level, unsigned gpte)
+{
+	unsigned index;
+
+	index = level - 1;
+	index |= (gpte & PT_PAGE_SIZE_MASK) >> (PT_PAGE_SIZE_SHIFT - 2);
+	return mmu->last_pte_bitmap & (1 << index);
+}
+
 #define PTTYPE 64
 #include "paging_tmpl.h"
 #undef PTTYPE
@@ -3548,6 +3557,24 @@ static void update_permission_bitmask(struct kvm_vcpu *vcpu, struct kvm_mmu *mmu
 	}
 }
 
+static void update_last_pte_bitmap(struct kvm_vcpu *vcpu, struct kvm_mmu *mmu)
+{
+	u8 map;
+	unsigned level, root_level = mmu->root_level;
+	const unsigned ps_set_index = 1 << 2;  /* bit 2 of index: ps */
+
+	if (root_level == PT32E_ROOT_LEVEL)
+		--root_level;
+	/* PT_PAGE_TABLE_LEVEL always terminates */
+	map = 1 | (1 << ps_set_index);
+	for (level = PT_DIRECTORY_LEVEL; level <= root_level; ++level) {
+		if (level <= PT_PDPE_LEVEL
+		    && (mmu->root_level >= PT32E_ROOT_LEVEL || is_pse(vcpu)))
+			map |= 1 << (ps_set_index | (level - 1));
+	}
+	mmu->last_pte_bitmap = map;
+}
+
 static int paging64_init_context_common(struct kvm_vcpu *vcpu,
 					struct kvm_mmu *context,
 					int level)
@@ -3557,6 +3584,7 @@ static int paging64_init_context_common(struct kvm_vcpu *vcpu,
 
 	reset_rsvds_bits_mask(vcpu, context);
 	update_permission_bitmask(vcpu, context);
+	update_last_pte_bitmap(vcpu, context);
 
 	ASSERT(is_pae(vcpu));
 	context->new_cr3 = paging_new_cr3;
@@ -3586,6 +3614,7 @@ static int paging32_init_context(struct kvm_vcpu *vcpu,
 
 	reset_rsvds_bits_mask(vcpu, context);
 	update_permission_bitmask(vcpu, context);
+	update_last_pte_bitmap(vcpu, context);
 
 	context->new_cr3 = paging_new_cr3;
 	context->page_fault = paging32_page_fault;
@@ -3647,6 +3676,7 @@ static int init_kvm_tdp_mmu(struct kvm_vcpu *vcpu)
 	}
 
 	update_permission_bitmask(vcpu, context);
+	update_last_pte_bitmap(vcpu, context);
 
 	return 0;
 }
@@ -3724,6 +3754,7 @@ static int init_kvm_nested_mmu(struct kvm_vcpu *vcpu)
 	}
 
 	update_permission_bitmask(vcpu, g_context);
+	update_last_pte_bitmap(vcpu, g_context);
 
 	return 0;
 }
diff --git a/arch/x86/kvm/mmu.h b/arch/x86/kvm/mmu.h
index 143ee70..b08dd34 100644
--- a/arch/x86/kvm/mmu.h
+++ b/arch/x86/kvm/mmu.h
@@ -20,7 +20,8 @@
 #define PT_ACCESSED_MASK (1ULL << PT_ACCESSED_SHIFT)
 #define PT_DIRTY_SHIFT 6
 #define PT_DIRTY_MASK (1ULL << PT_DIRTY_SHIFT)
-#define PT_PAGE_SIZE_MASK (1ULL << 7)
+#define PT_PAGE_SIZE_SHIFT 7
+#define PT_PAGE_SIZE_MASK (1ULL << PT_PAGE_SIZE_SHIFT)
 #define PT_PAT_MASK (1ULL << 7)
 #define PT_GLOBAL_MASK (1ULL << 8)
 #define PT64_NX_SHIFT 63
diff --git a/arch/x86/kvm/paging_tmpl.h b/arch/x86/kvm/paging_tmpl.h
index eb4a668..ec1e101 100644
--- a/arch/x86/kvm/paging_tmpl.h
+++ b/arch/x86/kvm/paging_tmpl.h
@@ -101,24 +101,6 @@ static int FNAME(cmpxchg_gpte)(struct kvm_vcpu *vcpu, struct kvm_mmu *mmu,
 	return (ret != orig_pte);
 }
 
-static bool FNAME(is_last_gpte)(struct guest_walker *walker,
-				struct kvm_vcpu *vcpu, struct kvm_mmu *mmu,
-				pt_element_t gpte)
-{
-	if (walker->level == PT_PAGE_TABLE_LEVEL)
-		return true;
-
-	if ((walker->level == PT_DIRECTORY_LEVEL) && is_large_pte(gpte) &&
-	    (PTTYPE == 64 || is_pse(vcpu)))
-		return true;
-
-	if ((walker->level == PT_PDPE_LEVEL) && is_large_pte(gpte) &&
-	    (mmu->root_level == PT64_ROOT_LEVEL))
-		return true;
-
-	return false;
-}
-
 /*
  * Fetch a guest pte for a guest virtual address
  */
@@ -219,9 +201,7 @@ retry_walk:
 			mark_page_dirty(vcpu->kvm, table_gfn);
 			pte |= PT_ACCESSED_MASK;
 		}
 
 		walker->ptes[walker->level - 1] = pte;
-	} while (!FNAME(is_last_gpte)(walker, vcpu, mmu, pte));
+	} while (is_last_gpte(mmu, walker->level, pte));
 
 	if (unlikely(eperm)) {
 		errcode |= PFERR_PRESENT_MASK;
-- 


-- 
error compiling committee.c: too many arguments to function