diff mbox series

[v3,6/8] KVM: x86/mmu: Skip rmap operations if rmaps not allocated

Message ID 20210506184241.618958-7-bgardon@google.com (mailing list archive)
State New, archived
Headers show
Series Lazily allocate memslot rmaps | expand

Commit Message

Ben Gardon May 6, 2021, 6:42 p.m. UTC 
If only the TDP MMU is being used to manage the memory mappings for a VM,
then many rmap operations can be skipped as they are guaranteed to be
no-ops. This saves some time which would be spent on the rmap operation.
It also avoids acquiring the MMU lock in write mode for many operations.

This makes it safe to run the VM without rmaps allocated, when only
using the TDP MMU and sets the stage for waiting to allocate the rmaps
until they're needed.

Signed-off-by: Ben Gardon <bgardon@google.com>
---
 arch/x86/kvm/mmu/mmu.c | 128 +++++++++++++++++++++++++----------------
 1 file changed, 77 insertions(+), 51 deletions(-)

Comments

kernel test robot May 6, 2021, 11:07 p.m. UTC | #1 
Hi Ben,

Thank you for the patch! Perhaps something to improve:

[auto build test WARNING on kvm/queue]
[also build test WARNING on tip/master linus/master next-20210506]
[cannot apply to linux/master v5.12]
[If your patch is applied to the wrong git tree, kindly drop us a note.
And when submitting patch, we suggest to use '--base' as documented in
https://git-scm.com/docs/git-format-patch]

url:    https://github.com/0day-ci/linux/commits/Ben-Gardon/Lazily-allocate-memslot-rmaps/20210507-024533
base:   https://git.kernel.org/pub/scm/virt/kvm/kvm.git queue
config: x86_64-randconfig-s021-20210506 (attached as .config)
compiler: gcc-9 (Debian 9.3.0-22) 9.3.0
reproduce:
        # apt-get install sparse
        # sparse version: v0.6.3-341-g8af24329-dirty
        # https://github.com/0day-ci/linux/commit/c7c4f34907c708172e52fb04dc753a917a5eebb6
        git remote add linux-review https://github.com/0day-ci/linux
        git fetch --no-tags linux-review Ben-Gardon/Lazily-allocate-memslot-rmaps/20210507-024533
        git checkout c7c4f34907c708172e52fb04dc753a917a5eebb6
        # save the attached .config to linux build tree
        make W=1 C=1 CF='-fdiagnostic-prefix -D__CHECK_ENDIAN__' W=1 ARCH=x86_64 

If you fix the issue, kindly add following tag as appropriate
Reported-by: kernel test robot <lkp@intel.com>


sparse warnings: (new ones prefixed by >>)
   arch/x86/kvm/mmu/mmu.c: note: in included file (through include/linux/kvm_host.h, arch/x86/kvm/irq.h):
>> arch/x86/include/asm/kvm_host.h:1871:36: sparse: sparse: marked inline, but without a definition
>> arch/x86/include/asm/kvm_host.h:1871:36: sparse: sparse: marked inline, but without a definition
>> arch/x86/include/asm/kvm_host.h:1871:36: sparse: sparse: marked inline, but without a definition
>> arch/x86/include/asm/kvm_host.h:1871:36: sparse: sparse: marked inline, but without a definition
>> arch/x86/include/asm/kvm_host.h:1871:36: sparse: sparse: marked inline, but without a definition
>> arch/x86/include/asm/kvm_host.h:1871:36: sparse: sparse: marked inline, but without a definition
>> arch/x86/include/asm/kvm_host.h:1871:36: sparse: sparse: marked inline, but without a definition
>> arch/x86/include/asm/kvm_host.h:1871:36: sparse: sparse: marked inline, but without a definition
>> arch/x86/include/asm/kvm_host.h:1871:36: sparse: sparse: marked inline, but without a definition
>> arch/x86/include/asm/kvm_host.h:1871:36: sparse: sparse: marked inline, but without a definition
>> arch/x86/include/asm/kvm_host.h:1871:36: sparse: sparse: marked inline, but without a definition
>> arch/x86/include/asm/kvm_host.h:1871:36: sparse: sparse: marked inline, but without a definition
>> arch/x86/include/asm/kvm_host.h:1871:36: sparse: sparse: marked inline, but without a definition

vim +1871 arch/x86/include/asm/kvm_host.h

fb04a1eddb1a65 Peter Xu   2020-09-30  1870  
fac0d516d29b67 Ben Gardon 2021-05-06 @1871  inline bool kvm_memslots_have_rmaps(struct kvm *kvm);
fac0d516d29b67 Ben Gardon 2021-05-06  1872  

---
0-DAY CI Kernel Test Service, Intel Corporation
https://lists.01.org/hyperkitty/list/kbuild-all@lists.01.org
diff mbox series

Patch

diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index 8761b4925755..730ea84bf7e7 100644
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -1189,6 +1189,10 @@  static void kvm_mmu_write_protect_pt_masked(struct kvm *kvm,
 	if (is_tdp_mmu_enabled(kvm))
 		kvm_tdp_mmu_clear_dirty_pt_masked(kvm, slot,
 				slot->base_gfn + gfn_offset, mask, true);
+
+	if (!kvm_memslots_have_rmaps(kvm))
+		return;
+
 	while (mask) {
 		rmap_head = __gfn_to_rmap(slot->base_gfn + gfn_offset + __ffs(mask),
 					  PG_LEVEL_4K, slot);
@@ -1218,6 +1222,10 @@  static void kvm_mmu_clear_dirty_pt_masked(struct kvm *kvm,
 	if (is_tdp_mmu_enabled(kvm))
 		kvm_tdp_mmu_clear_dirty_pt_masked(kvm, slot,
 				slot->base_gfn + gfn_offset, mask, false);
+
+	if (!kvm_memslots_have_rmaps(kvm))
+		return;
+
 	while (mask) {
 		rmap_head = __gfn_to_rmap(slot->base_gfn + gfn_offset + __ffs(mask),
 					  PG_LEVEL_4K, slot);
@@ -1260,9 +1268,12 @@  bool kvm_mmu_slot_gfn_write_protect(struct kvm *kvm,
 	int i;
 	bool write_protected = false;
 
-	for (i = PG_LEVEL_4K; i <= KVM_MAX_HUGEPAGE_LEVEL; ++i) {
-		rmap_head = __gfn_to_rmap(gfn, i, slot);
-		write_protected |= __rmap_write_protect(kvm, rmap_head, true);
+	if (kvm_memslots_have_rmaps(kvm)) {
+		for (i = PG_LEVEL_4K; i <= KVM_MAX_HUGEPAGE_LEVEL; ++i) {
+			rmap_head = __gfn_to_rmap(gfn, i, slot);
+			write_protected |= __rmap_write_protect(kvm, rmap_head,
+								true);
+		}
 	}
 
 	if (is_tdp_mmu_enabled(kvm))
@@ -1433,9 +1444,10 @@  static __always_inline bool kvm_handle_gfn_range(struct kvm *kvm,
 
 bool kvm_unmap_gfn_range(struct kvm *kvm, struct kvm_gfn_range *range)
 {
-	bool flush;
+	bool flush = false;
 
-	flush = kvm_handle_gfn_range(kvm, range, kvm_unmap_rmapp);
+	if (kvm_memslots_have_rmaps(kvm))
+		flush = kvm_handle_gfn_range(kvm, range, kvm_unmap_rmapp);
 
 	if (is_tdp_mmu_enabled(kvm))
 		flush |= kvm_tdp_mmu_unmap_gfn_range(kvm, range, flush);
@@ -1445,9 +1457,10 @@  bool kvm_unmap_gfn_range(struct kvm *kvm, struct kvm_gfn_range *range)
 
 bool kvm_set_spte_gfn(struct kvm *kvm, struct kvm_gfn_range *range)
 {
-	bool flush;
+	bool flush = false;
 
-	flush = kvm_handle_gfn_range(kvm, range, kvm_set_pte_rmapp);
+	if (kvm_memslots_have_rmaps(kvm))
+		flush = kvm_handle_gfn_range(kvm, range, kvm_set_pte_rmapp);
 
 	if (is_tdp_mmu_enabled(kvm))
 		flush |= kvm_tdp_mmu_set_spte_gfn(kvm, range);
@@ -1500,9 +1513,10 @@  static void rmap_recycle(struct kvm_vcpu *vcpu, u64 *spte, gfn_t gfn)
 
 bool kvm_age_gfn(struct kvm *kvm, struct kvm_gfn_range *range)
 {
-	bool young;
+	bool young = false;
 
-	young = kvm_handle_gfn_range(kvm, range, kvm_age_rmapp);
+	if (kvm_memslots_have_rmaps(kvm))
+		young = kvm_handle_gfn_range(kvm, range, kvm_age_rmapp);
 
 	if (is_tdp_mmu_enabled(kvm))
 		young |= kvm_tdp_mmu_age_gfn_range(kvm, range);
@@ -1512,9 +1526,10 @@  bool kvm_age_gfn(struct kvm *kvm, struct kvm_gfn_range *range)
 
 bool kvm_test_age_gfn(struct kvm *kvm, struct kvm_gfn_range *range)
 {
-	bool young;
+	bool young = false;
 
-	young = kvm_handle_gfn_range(kvm, range, kvm_test_age_rmapp);
+	if (kvm_memslots_have_rmaps(kvm))
+		young = kvm_handle_gfn_range(kvm, range, kvm_test_age_rmapp);
 
 	if (is_tdp_mmu_enabled(kvm))
 		young |= kvm_tdp_mmu_test_age_gfn(kvm, range);
@@ -5440,7 +5455,8 @@  static void kvm_mmu_zap_all_fast(struct kvm *kvm)
 	 */
 	kvm_reload_remote_mmus(kvm);
 
-	kvm_zap_obsolete_pages(kvm);
+	if (kvm_memslots_have_rmaps(kvm))
+		kvm_zap_obsolete_pages(kvm);
 
 	write_unlock(&kvm->mmu_lock);
 
@@ -5492,29 +5508,29 @@  void kvm_zap_gfn_range(struct kvm *kvm, gfn_t gfn_start, gfn_t gfn_end)
 	int i;
 	bool flush = false;
 
-	write_lock(&kvm->mmu_lock);
-	for (i = 0; i < KVM_ADDRESS_SPACE_NUM; i++) {
-		slots = __kvm_memslots(kvm, i);
-		kvm_for_each_memslot(memslot, slots) {
-			gfn_t start, end;
-
-			start = max(gfn_start, memslot->base_gfn);
-			end = min(gfn_end, memslot->base_gfn + memslot->npages);
-			if (start >= end)
-				continue;
+	if (kvm_memslots_have_rmaps(kvm)) {
+		write_lock(&kvm->mmu_lock);
+		for (i = 0; i < KVM_ADDRESS_SPACE_NUM; i++) {
+			slots = __kvm_memslots(kvm, i);
+			kvm_for_each_memslot(memslot, slots) {
+				gfn_t start, end;
+
+				start = max(gfn_start, memslot->base_gfn);
+				end = min(gfn_end, memslot->base_gfn + memslot->npages);
+				if (start >= end)
+					continue;
 
-			flush = slot_handle_level_range(kvm, memslot, kvm_zap_rmapp,
-							PG_LEVEL_4K,
-							KVM_MAX_HUGEPAGE_LEVEL,
-							start, end - 1, true, flush);
+				flush = slot_handle_level_range(kvm, memslot,
+						kvm_zap_rmapp, PG_LEVEL_4K,
+						KVM_MAX_HUGEPAGE_LEVEL, start,
+						end - 1, true, flush);
+			}
 		}
+		if (flush)
+			kvm_flush_remote_tlbs_with_address(kvm, gfn_start, gfn_end);
+		write_unlock(&kvm->mmu_lock);
 	}
 
-	if (flush)
-		kvm_flush_remote_tlbs_with_address(kvm, gfn_start, gfn_end);
-
-	write_unlock(&kvm->mmu_lock);
-
 	if (is_tdp_mmu_enabled(kvm)) {
 		flush = false;
 
@@ -5541,12 +5557,15 @@  void kvm_mmu_slot_remove_write_access(struct kvm *kvm,
 				      struct kvm_memory_slot *memslot,
 				      int start_level)
 {
-	bool flush;
+	bool flush = false;
 
-	write_lock(&kvm->mmu_lock);
-	flush = slot_handle_level(kvm, memslot, slot_rmap_write_protect,
-				start_level, KVM_MAX_HUGEPAGE_LEVEL, false);
-	write_unlock(&kvm->mmu_lock);
+	if (kvm_memslots_have_rmaps(kvm)) {
+		write_lock(&kvm->mmu_lock);
+		flush = slot_handle_level(kvm, memslot, slot_rmap_write_protect,
+					  start_level, KVM_MAX_HUGEPAGE_LEVEL,
+					  false);
+		write_unlock(&kvm->mmu_lock);
+	}
 
 	if (is_tdp_mmu_enabled(kvm)) {
 		read_lock(&kvm->mmu_lock);
@@ -5616,16 +5635,15 @@  void kvm_mmu_zap_collapsible_sptes(struct kvm *kvm,
 	struct kvm_memory_slot *slot = (struct kvm_memory_slot *)memslot;
 	bool flush;
 
-	write_lock(&kvm->mmu_lock);
-	flush = slot_handle_leaf(kvm, slot, kvm_mmu_zap_collapsible_spte, true);
-
-	if (flush)
-		kvm_arch_flush_remote_tlbs_memslot(kvm, slot);
-	write_unlock(&kvm->mmu_lock);
+	if (kvm_memslots_have_rmaps(kvm)) {
+		write_lock(&kvm->mmu_lock);
+		flush = slot_handle_leaf(kvm, slot, kvm_mmu_zap_collapsible_spte, true);
+		if (flush)
+			kvm_arch_flush_remote_tlbs_memslot(kvm, slot);
+		write_unlock(&kvm->mmu_lock);
+	}
 
 	if (is_tdp_mmu_enabled(kvm)) {
-		flush = false;
-
 		read_lock(&kvm->mmu_lock);
 		flush = kvm_tdp_mmu_zap_collapsible_sptes(kvm, slot, flush);
 		if (flush)
@@ -5652,11 +5670,14 @@  void kvm_arch_flush_remote_tlbs_memslot(struct kvm *kvm,
 void kvm_mmu_slot_leaf_clear_dirty(struct kvm *kvm,
 				   struct kvm_memory_slot *memslot)
 {
-	bool flush;
+	bool flush = false;
 
-	write_lock(&kvm->mmu_lock);
-	flush = slot_handle_leaf(kvm, memslot, __rmap_clear_dirty, false);
-	write_unlock(&kvm->mmu_lock);
+	if (kvm_memslots_have_rmaps(kvm)) {
+		write_lock(&kvm->mmu_lock);
+		flush = slot_handle_leaf(kvm, memslot, __rmap_clear_dirty,
+					 false);
+		write_unlock(&kvm->mmu_lock);
+	}
 
 	if (is_tdp_mmu_enabled(kvm)) {
 		read_lock(&kvm->mmu_lock);
@@ -5681,6 +5702,14 @@  void kvm_mmu_zap_all(struct kvm *kvm)
 	int ign;
 
 	write_lock(&kvm->mmu_lock);
+	if (is_tdp_mmu_enabled(kvm))
+		kvm_tdp_mmu_zap_all(kvm);
+
+	if (!kvm_memslots_have_rmaps(kvm)) {
+		write_unlock(&kvm->mmu_lock);
+		return;
+	}
+
 restart:
 	list_for_each_entry_safe(sp, node, &kvm->arch.active_mmu_pages, link) {
 		if (WARN_ON(sp->role.invalid))
@@ -5693,9 +5722,6 @@  void kvm_mmu_zap_all(struct kvm *kvm)
 
 	kvm_mmu_commit_zap_page(kvm, &invalid_list);
 
-	if (is_tdp_mmu_enabled(kvm))
-		kvm_tdp_mmu_zap_all(kvm);
-
 	write_unlock(&kvm->mmu_lock);
 }