[PATCH v5 0/5] KVM: Dirty quota-based throttling

[PATCH v5 0/5] KVM: Dirty quota-based throttling

[Shivam Kumar]

This is v5 of the dirty quota series, with the following changes over v4:

1. x86-specific changes separated into a new commit. 
2. KVM requests used to handle dirty quota exit conditions.

v1:
https://lore.kernel.org/kvm/20211114145721.209219-1-shivam.kumar1@nutanix.com/
v2: https://lore.kernel.org/kvm/Ydx2EW6U3fpJoJF0@google.com/T/
v3: https://lore.kernel.org/kvm/YkT1kzWidaRFdQQh@google.com/T/
v4:
https://lore.kernel.org/all/20220521202937.184189-1-shivam.kumar1@nutanix.com/

Thanks,
Shivam

Shivam Kumar (5):
  KVM: Implement dirty quota-based throttling of vcpus
  KVM: x86: Dirty quota-based throttling of vcpus
  KVM: arm64: Dirty quota-based throttling of vcpus
  KVM: s390x: Dirty quota-based throttling of vcpus
  KVM: selftests: Add selftests for dirty quota throttling

 Documentation/virt/kvm/api.rst                | 32 +++++++++++++++++
 arch/arm64/kvm/arm.c                          |  9 +++++
 arch/s390/kvm/kvm-s390.c                      |  9 +++++
 arch/x86/kvm/mmu/spte.c                       |  4 +--
 arch/x86/kvm/vmx/vmx.c                        |  3 ++
 arch/x86/kvm/x86.c                            |  9 +++++
 include/linux/kvm_host.h                      | 20 ++++++++++-
 include/linux/kvm_types.h                     |  1 +
 include/uapi/linux/kvm.h                      | 12 +++++++
 tools/testing/selftests/kvm/dirty_log_test.c  | 33 +++++++++++++++--
 .../selftests/kvm/include/kvm_util_base.h     |  4 +++
 tools/testing/selftests/kvm/lib/kvm_util.c    | 36 +++++++++++++++++++
 virt/kvm/kvm_main.c                           | 26 ++++++++++++--
 13 files changed, 190 insertions(+), 8 deletions(-)

-- 
2.22.3

[PATCH v5 1/5] KVM: Implement dirty quota-based throttling of vcpus

[Shivam Kumar]

Define variables to track and throttle memory dirtying for every vcpu.

dirty_count:    Number of pages the vcpu has dirtied since its creation,
                while dirty logging is enabled.
dirty_quota:    Number of pages the vcpu is allowed to dirty. To dirty
                more, it needs to request more quota by exiting to
                userspace.

Implement the flow for throttling based on dirty quota.

i) Increment dirty_count for the vcpu whenever it dirties a page.
ii) Exit to userspace whenever the dirty quota is exhausted (i.e. dirty
count equals/exceeds dirty quota) to request more dirty quota.

Suggested-by: Shaju Abraham <shaju.abraham@nutanix.com>
Suggested-by: Manish Mishra <manish.mishra@nutanix.com>
Co-developed-by: Anurag Madnawat <anurag.madnawat@nutanix.com>
Signed-off-by: Anurag Madnawat <anurag.madnawat@nutanix.com>
Signed-off-by: Shivam Kumar <shivam.kumar1@nutanix.com>
---
 Documentation/virt/kvm/api.rst | 32 ++++++++++++++++++++++++++++++++
 include/linux/kvm_host.h       | 20 +++++++++++++++++++-
 include/linux/kvm_types.h      |  1 +
 include/uapi/linux/kvm.h       | 12 ++++++++++++
 virt/kvm/kvm_main.c            | 26 +++++++++++++++++++++++---
 5 files changed, 87 insertions(+), 4 deletions(-)

diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst
index abd7c32126ce..2d7f63aa6ef3 100644
--- a/Documentation/virt/kvm/api.rst
+++ b/Documentation/virt/kvm/api.rst
@@ -6614,6 +6614,24 @@ array field represents return values. The userspace should update the return
 values of SBI call before resuming the VCPU. For more details on RISC-V SBI
 spec refer, https://github.com/riscv/riscv-sbi-doc.
 
+::
+
+		/* KVM_EXIT_DIRTY_QUOTA_EXHAUSTED */
+		struct {
+			__u64 count;
+			__u64 quota;
+		} dirty_quota_exit;
+If exit reason is KVM_EXIT_DIRTY_QUOTA_EXHAUSTED, it indicates that the VCPU has
+exhausted its dirty quota. The 'dirty_quota_exit' member of kvm_run structure
+makes the following information available to the userspace:
+	'count' field: the current count of pages dirtied by the VCPU, can be
+        skewed based on the size of the pages accessed by each vCPU.
+	'quota' field: the observed dirty quota just before the exit to userspace.
+The userspace can design a strategy to allocate the overall scope of dirtying
+for the VM among the vcpus. Based on the strategy and the current state of dirty
+quota throttling, the userspace can make a decision to either update (increase)
+the quota or to put the VCPU to sleep for some time.
+
 ::
 
     /* KVM_EXIT_NOTIFY */
@@ -6668,6 +6686,20 @@ values in kvm_run even if the corresponding bit in kvm_dirty_regs is not set.
 
 ::
 
+	/*
+	 * Number of pages the vCPU is allowed to have dirtied over its entire
+	 * lifetime.  KVM_RUN exits with KVM_EXIT_DIRTY_QUOTA_EXHAUSTED if the quota
+	 * is reached/exceeded.
+	 */
+	__u64 dirty_quota;
+Please note that enforcing the quota is best effort, as the guest may dirty
+multiple pages before KVM can recheck the quota.  However, unless KVM is using
+a hardware-based dirty ring buffer, e.g. Intel's Page Modification Logging,
+KVM will detect quota exhaustion within a handful of dirtied page.  If a
+hardware ring buffer is used, the overrun is bounded by the size of the buffer
+(512 entries for PML).
+
+::
   };
 
 
diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index f4519d3689e1..9acb28635d94 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -151,12 +151,13 @@ static inline bool is_error_page(struct page *page)
 #define KVM_REQUEST_NO_ACTION      BIT(10)
 /*
  * Architecture-independent vcpu->requests bit members
- * Bits 4-7 are reserved for more arch-independent bits.
+ * Bits 5-7 are reserved for more arch-independent bits.
  */
 #define KVM_REQ_TLB_FLUSH         (0 | KVM_REQUEST_WAIT | KVM_REQUEST_NO_WAKEUP)
 #define KVM_REQ_VM_DEAD           (1 | KVM_REQUEST_WAIT | KVM_REQUEST_NO_WAKEUP)
 #define KVM_REQ_UNBLOCK           2
 #define KVM_REQ_UNHALT            3
+#define KVM_REQ_DIRTY_QUOTA_EXIT  4
 #define KVM_REQUEST_ARCH_BASE     8
 
 /*
@@ -380,6 +381,8 @@ struct kvm_vcpu {
 	 */
 	struct kvm_memory_slot *last_used_slot;
 	u64 last_used_slot_gen;
+
+	u64 dirty_quota;
 };
 
 /*
@@ -542,6 +545,21 @@ static inline int kvm_vcpu_exiting_guest_mode(struct kvm_vcpu *vcpu)
 	return cmpxchg(&vcpu->mode, IN_GUEST_MODE, EXITING_GUEST_MODE);
 }
 
+static inline int kvm_vcpu_check_dirty_quota(struct kvm_vcpu *vcpu)
+{
+	struct kvm_run *run = vcpu->run;
+	u64 dirty_quota = READ_ONCE(run->dirty_quota);
+	u64 pages_dirtied = vcpu->stat.generic.pages_dirtied;
+
+	if (!dirty_quota || (pages_dirtied < dirty_quota))
+		return 1;
+
+	run->exit_reason = KVM_EXIT_DIRTY_QUOTA_EXHAUSTED;
+	run->dirty_quota_exit.count = pages_dirtied;
+	run->dirty_quota_exit.quota = dirty_quota;
+	return 0;
+}
+
 /*
  * Some of the bitops functions do not support too long bitmaps.
  * This number must be determined not to exceed such limits.
diff --git a/include/linux/kvm_types.h b/include/linux/kvm_types.h
index 3ca3db020e0e..263a588f3cd3 100644
--- a/include/linux/kvm_types.h
+++ b/include/linux/kvm_types.h
@@ -118,6 +118,7 @@ struct kvm_vcpu_stat_generic {
 	u64 halt_poll_fail_hist[HALT_POLL_HIST_COUNT];
 	u64 halt_wait_hist[HALT_POLL_HIST_COUNT];
 	u64 blocking;
+	u64 pages_dirtied;
 };
 
 #define KVM_STATS_NAME_SIZE	48
diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
index eed0315a77a6..4c4a65b0f0a5 100644
--- a/include/uapi/linux/kvm.h
+++ b/include/uapi/linux/kvm.h
@@ -272,6 +272,7 @@ struct kvm_xen_exit {
 #define KVM_EXIT_RISCV_SBI        35
 #define KVM_EXIT_RISCV_CSR        36
 #define KVM_EXIT_NOTIFY           37
+#define KVM_EXIT_DIRTY_QUOTA_EXHAUSTED 38
 
 /* For KVM_EXIT_INTERNAL_ERROR */
 /* Emulate instruction failed. */
@@ -510,6 +511,11 @@ struct kvm_run {
 #define KVM_NOTIFY_CONTEXT_INVALID	(1 << 0)
 			__u32 flags;
 		} notify;
+		/* KVM_EXIT_DIRTY_QUOTA_EXHAUSTED */
+		struct {
+			__u64 count;
+			__u64 quota;
+		} dirty_quota_exit;
 		/* Fix the size of the union. */
 		char padding[256];
 	};
@@ -531,6 +537,12 @@ struct kvm_run {
 		struct kvm_sync_regs regs;
 		char padding[SYNC_REGS_SIZE_BYTES];
 	} s;
+	/*
+	 * Number of pages the vCPU is allowed to have dirtied over its entire
+	 * lifetime.  KVM_RUN exits with KVM_EXIT_DIRTY_QUOTA_EXHAUSTED if the
+	 * quota is reached/exceeded.
+	 */
+	__u64 dirty_quota;
 };
 
 /* for KVM_REGISTER_COALESCED_MMIO / KVM_UNREGISTER_COALESCED_MMIO */
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 584a5bab3af3..f315af50037d 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -3298,18 +3298,36 @@ int kvm_clear_guest(struct kvm *kvm, gpa_t gpa, unsigned long len)
 }
 EXPORT_SYMBOL_GPL(kvm_clear_guest);
 
+static void kvm_vcpu_is_dirty_quota_exhausted(struct kvm_vcpu *vcpu)
+{
+	u64 dirty_quota = READ_ONCE(vcpu->run->dirty_quota);
+
+	if (!dirty_quota || (vcpu->stat.generic.pages_dirtied < dirty_quota))
+		return;
+
+	/*
+	 * Snapshot the quota to report it to userspace.  The dirty count will be
+	 * captured when the request is processed.
+	 */
+	vcpu->dirty_quota = dirty_quota;
+	kvm_make_request(KVM_REQ_DIRTY_QUOTA_EXIT, vcpu);
+}
+
 void mark_page_dirty_in_slot(struct kvm *kvm,
 			     const struct kvm_memory_slot *memslot,
 		 	     gfn_t gfn)
 {
 	struct kvm_vcpu *vcpu = kvm_get_running_vcpu();
 
-#ifdef CONFIG_HAVE_KVM_DIRTY_RING
 	if (WARN_ON_ONCE(!vcpu) || WARN_ON_ONCE(vcpu->kvm != kvm))
 		return;
-#endif
 
-	if (memslot && kvm_slot_dirty_track_enabled(memslot)) {
+	if (!memslot)
+		return;
+
+	WARN_ON_ONCE(!vcpu->stat.generic.pages_dirtied++);
+
+	if (kvm_slot_dirty_track_enabled(memslot)) {
 		unsigned long rel_gfn = gfn - memslot->base_gfn;
 		u32 slot = (memslot->as_id << 16) | memslot->id;
 
@@ -3318,6 +3336,8 @@ void mark_page_dirty_in_slot(struct kvm *kvm,
 					    slot, rel_gfn);
 		else
 			set_bit_le(rel_gfn, memslot->dirty_bitmap);
+
+		kvm_vcpu_is_dirty_quota_exhausted(vcpu);
 	}
 }
 EXPORT_SYMBOL_GPL(mark_page_dirty_in_slot);
-- 
2.22.3

Re: [PATCH v5 1/5] KVM: Implement dirty quota-based throttling of vcpus

[kernel test robot]

Hi Shivam,

Thank you for the patch! Perhaps something to improve:

[auto build test WARNING on kvm/queue]
[also build test WARNING on mst-vhost/linux-next linus/master v6.0-rc5 next-20220912]
[cannot apply to kvms390/next]
[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#_base_tree_information]

url:    https://github.com/intel-lab-lkp/linux/commits/Shivam-Kumar/KVM-Dirty-quota-based-throttling/20220912-123509
base:   https://git.kernel.org/pub/scm/virt/kvm/kvm.git queue
reproduce:
        # https://github.com/intel-lab-lkp/linux/commit/772b4ec9f5aee3af7759fe673b6c1e157e7afb8d
        git remote add linux-review https://github.com/intel-lab-lkp/linux
        git fetch --no-tags linux-review Shivam-Kumar/KVM-Dirty-quota-based-throttling/20220912-123509
        git checkout 772b4ec9f5aee3af7759fe673b6c1e157e7afb8d
        make menuconfig
        # enable CONFIG_COMPILE_TEST, CONFIG_WARN_MISSING_DOCUMENTS, CONFIG_WARN_ABI_ERRORS
        make htmldocs

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

All warnings (new ones prefixed by >>):

>> Documentation/virt/kvm/api.rst:6630: WARNING: Block quote ends without a blank line; unexpected unindent.

vim +6630 Documentation/virt/kvm/api.rst

  6618	
  6619			/* KVM_EXIT_DIRTY_QUOTA_EXHAUSTED */
  6620			struct {
  6621				__u64 count;
  6622				__u64 quota;
  6623			} dirty_quota_exit;
  6624	If exit reason is KVM_EXIT_DIRTY_QUOTA_EXHAUSTED, it indicates that the VCPU has
  6625	exhausted its dirty quota. The 'dirty_quota_exit' member of kvm_run structure
  6626	makes the following information available to the userspace:
  6627		'count' field: the current count of pages dirtied by the VCPU, can be
  6628	        skewed based on the size of the pages accessed by each vCPU.
  6629		'quota' field: the observed dirty quota just before the exit to userspace.
> 6630	The userspace can design a strategy to allocate the overall scope of dirtying
  6631	for the VM among the vcpus. Based on the strategy and the current state of dirty
  6632	quota throttling, the userspace can make a decision to either update (increase)
  6633	the quota or to put the VCPU to sleep for some time.
  6634	

-- 
0-DAY CI Kernel Test Service
https://01.org/lkp

[PATCH v5 2/5] KVM: x86: Dirty quota-based throttling of vcpus

[Shivam Kumar]

Exit to userspace whenever the dirty quota is exhausted (i.e. dirty count
equals/exceeds dirty quota) to request more dirty quota.

Suggested-by: Shaju Abraham <shaju.abraham@nutanix.com>
Suggested-by: Manish Mishra <manish.mishra@nutanix.com>
Co-developed-by: Anurag Madnawat <anurag.madnawat@nutanix.com>
Signed-off-by: Anurag Madnawat <anurag.madnawat@nutanix.com>
Signed-off-by: Shivam Kumar <shivam.kumar1@nutanix.com>
---
 arch/x86/kvm/mmu/spte.c | 4 ++--
 arch/x86/kvm/vmx/vmx.c  | 3 +++
 arch/x86/kvm/x86.c      | 9 +++++++++
 3 files changed, 14 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kvm/mmu/spte.c b/arch/x86/kvm/mmu/spte.c
index 2e08b2a45361..c0ed35abbf2d 100644
--- a/arch/x86/kvm/mmu/spte.c
+++ b/arch/x86/kvm/mmu/spte.c
@@ -228,9 +228,9 @@ bool make_spte(struct kvm_vcpu *vcpu, struct kvm_mmu_page *sp,
 		  "spte = 0x%llx, level = %d, rsvd bits = 0x%llx", spte, level,
 		  get_rsvd_bits(&vcpu->arch.mmu->shadow_zero_check, spte, level));
 
-	if ((spte & PT_WRITABLE_MASK) && kvm_slot_dirty_track_enabled(slot)) {
+	if (spte & PT_WRITABLE_MASK) {
 		/* Enforced by kvm_mmu_hugepage_adjust. */
-		WARN_ON(level > PG_LEVEL_4K);
+		WARN_ON(level > PG_LEVEL_4K && kvm_slot_dirty_track_enabled(slot));
 		mark_page_dirty_in_slot(vcpu->kvm, slot, gfn);
 	}
 
diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index d7f8331d6f7e..9499c7566479 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -5750,6 +5750,9 @@ static int handle_invalid_guest_state(struct kvm_vcpu *vcpu)
 		 */
 		if (__xfer_to_guest_mode_work_pending())
 			return 1;
+
+		if (!kvm_vcpu_check_dirty_quota(vcpu))
+			return 0;
 	}
 
 	return 1;
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 205ebdc2b11b..0b1243b598c9 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -10362,6 +10362,15 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu)
 			r = 0;
 			goto out;
 		}
+		if (kvm_check_request(KVM_REQ_DIRTY_QUOTA_EXIT, vcpu)) {
+			struct kvm_run *run = vcpu->run;
+
+			run->exit_reason = KVM_EXIT_DIRTY_QUOTA_EXHAUSTED;
+			run->dirty_quota_exit.count = vcpu->stat.generic.pages_dirtied;
+			run->dirty_quota_exit.quota = vcpu->dirty_quota;
+			r = 0;
+			goto out;
+		}
 
 		/*
 		 * KVM_REQ_HV_STIMER has to be processed after
-- 
2.22.3

[PATCH v5 3/5] KVM: arm64: Dirty quota-based throttling of vcpus

[Shivam Kumar]

Exit to userspace whenever the dirty quota is exhausted (i.e. dirty count
equals/exceeds dirty quota) to request more dirty quota.

Suggested-by: Shaju Abraham <shaju.abraham@nutanix.com>
Suggested-by: Manish Mishra <manish.mishra@nutanix.com>
Co-developed-by: Anurag Madnawat <anurag.madnawat@nutanix.com>
Signed-off-by: Anurag Madnawat <anurag.madnawat@nutanix.com>
Signed-off-by: Shivam Kumar <shivam.kumar1@nutanix.com>
---
 arch/arm64/kvm/arm.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c
index 2ff0ef62abad..ff17d14aa5b0 100644
--- a/arch/arm64/kvm/arm.c
+++ b/arch/arm64/kvm/arm.c
@@ -747,6 +747,15 @@ static int check_vcpu_requests(struct kvm_vcpu *vcpu)
 
 		if (kvm_check_request(KVM_REQ_SUSPEND, vcpu))
 			return kvm_vcpu_suspend(vcpu);
+
+		if (kvm_check_request(KVM_REQ_DIRTY_QUOTA_EXIT, vcpu)) {
+			struct kvm_run *run = vcpu->run;
+
+			run->exit_reason = KVM_EXIT_DIRTY_QUOTA_EXHAUSTED;
+			run->dirty_quota_exit.count = vcpu->stat.generic.pages_dirtied;
+			run->dirty_quota_exit.quota = vcpu->dirty_quota;
+			return 0;
+		}
 	}
 
 	return 1;
-- 
2.22.3

[PATCH v5 4/5] KVM: s390x: Dirty quota-based throttling of vcpus

[Shivam Kumar]

Exit to userspace whenever the dirty quota is exhausted (i.e. dirty count
equals/exceeds dirty quota) to request more dirty quota.

Suggested-by: Shaju Abraham <shaju.abraham@nutanix.com>
Suggested-by: Manish Mishra <manish.mishra@nutanix.com>
Co-developed-by: Anurag Madnawat <anurag.madnawat@nutanix.com>
Signed-off-by: Anurag Madnawat <anurag.madnawat@nutanix.com>
Signed-off-by: Shivam Kumar <shivam.kumar1@nutanix.com>
---
 arch/s390/kvm/kvm-s390.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
index edfd4bbd0cba..2fe2933a7064 100644
--- a/arch/s390/kvm/kvm-s390.c
+++ b/arch/s390/kvm/kvm-s390.c
@@ -4343,6 +4343,15 @@ static int kvm_s390_handle_requests(struct kvm_vcpu *vcpu)
 		goto retry;
 	}
 
+	if (kvm_check_request(KVM_REQ_DIRTY_QUOTA_EXIT, vcpu)) {
+		struct kvm_run *run = vcpu->run;
+
+		run->exit_reason = KVM_EXIT_DIRTY_QUOTA_EXHAUSTED;
+		run->dirty_quota_exit.count = vcpu->stat.generic.pages_dirtied;
+		run->dirty_quota_exit.quota = vcpu->dirty_quota;
+		return 1;
+	}
+
 	/* nothing to do, just clear the request */
 	kvm_clear_request(KVM_REQ_UNHALT, vcpu);
 	/* we left the vsie handler, nothing to do, just clear the request */
-- 
2.22.3

[PATCH v5 5/5] KVM: selftests: Add selftests for dirty quota throttling

[Shivam Kumar]

Add selftests for dirty quota throttling with an optional -d parameter
to configure by what value dirty quota should be incremented after
each dirty quota exit. With very small intervals, a smaller value of
dirty quota can ensure that the dirty quota exit code is tested. A zero
value disables dirty quota throttling and thus dirty logging, without
dirty quota throttling, can be tested.

Suggested-by: Shaju Abraham <shaju.abraham@nutanix.com>
Suggested-by: Manish Mishra <manish.mishra@nutanix.com>
Co-developed-by: Anurag Madnawat <anurag.madnawat@nutanix.com>
Signed-off-by: Anurag Madnawat <anurag.madnawat@nutanix.com>
Signed-off-by: Shivam Kumar <shivam.kumar1@nutanix.com>
---
 tools/testing/selftests/kvm/dirty_log_test.c  | 33 +++++++++++++++--
 .../selftests/kvm/include/kvm_util_base.h     |  4 +++
 tools/testing/selftests/kvm/lib/kvm_util.c    | 36 +++++++++++++++++++
 3 files changed, 71 insertions(+), 2 deletions(-)

diff --git a/tools/testing/selftests/kvm/dirty_log_test.c b/tools/testing/selftests/kvm/dirty_log_test.c
index 9c883c94d478..81c46eff7e1d 100644
--- a/tools/testing/selftests/kvm/dirty_log_test.c
+++ b/tools/testing/selftests/kvm/dirty_log_test.c
@@ -63,6 +63,8 @@
 
 #define SIG_IPI SIGUSR1
 
+#define TEST_DIRTY_QUOTA_INCREMENT		8
+
 /*
  * Guest/Host shared variables. Ensure addr_gva2hva() and/or
  * sync_global_to/from_guest() are used when accessing from
@@ -189,6 +191,7 @@ static enum log_mode_t host_log_mode_option = LOG_MODE_ALL;
 static enum log_mode_t host_log_mode;
 static pthread_t vcpu_thread;
 static uint32_t test_dirty_ring_count = TEST_DIRTY_RING_COUNT;
+static uint64_t test_dirty_quota_increment = TEST_DIRTY_QUOTA_INCREMENT;
 
 static void vcpu_kick(void)
 {
@@ -208,6 +211,13 @@ static void sem_wait_until(sem_t *sem)
 	while (ret == -1 && errno == EINTR);
 }
 
+static void set_dirty_quota(struct kvm_vm *vm, uint64_t dirty_quota)
+{
+	struct kvm_run *run = vcpu_state(vm, VCPU_ID);
+
+	vcpu_set_dirty_quota(run, dirty_quota);
+}
+
 static bool clear_log_supported(void)
 {
 	return kvm_has_cap(KVM_CAP_MANUAL_DIRTY_LOG_PROTECT2);
@@ -255,7 +265,11 @@ static void default_after_vcpu_run(struct kvm_vcpu *vcpu, int ret, int err)
 	TEST_ASSERT(ret == 0 || (ret == -1 && err == EINTR),
 		    "vcpu run failed: errno=%d", err);
 
-	TEST_ASSERT(get_ucall(vcpu, NULL) == UCALL_SYNC,
+	if (test_dirty_quota_increment &&
+		run->exit_reason == KVM_EXIT_DIRTY_QUOTA_EXHAUSTED)
+		vcpu_handle_dirty_quota_exit(run, test_dirty_quota_increment);
+	else
+		TEST_ASSERT(get_ucall(vcpu, NULL) == UCALL_SYNC,
 		    "Invalid guest sync status: exit_reason=%s\n",
 		    exit_reason_str(run->exit_reason));
 
@@ -372,6 +386,9 @@ static void dirty_ring_after_vcpu_run(struct kvm_vcpu *vcpu, int ret, int err)
 	if (get_ucall(vcpu, NULL) == UCALL_SYNC) {
 		/* We should allow this to continue */
 		;
+	} else if (test_dirty_quota_increment &&
+		run->exit_reason == KVM_EXIT_DIRTY_QUOTA_EXHAUSTED) {
+		vcpu_handle_dirty_quota_exit(run, test_dirty_quota_increment);
 	} else if (run->exit_reason == KVM_EXIT_DIRTY_RING_FULL ||
 		   (ret == -1 && err == EINTR)) {
 		/* Update the flag first before pause */
@@ -762,6 +779,10 @@ static void run_test(enum vm_guest_mode mode, void *arg)
 	sync_global_to_guest(vm, guest_test_virt_mem);
 	sync_global_to_guest(vm, guest_num_pages);
 
+	/* Initialise dirty quota */
+	if (test_dirty_quota_increment)
+		set_dirty_quota(vm, test_dirty_quota_increment);
+
 	/* Start the iterations */
 	iteration = 1;
 	sync_global_to_guest(vm, iteration);
@@ -803,6 +824,9 @@ static void run_test(enum vm_guest_mode mode, void *arg)
 	/* Tell the vcpu thread to quit */
 	host_quit = true;
 	log_mode_before_vcpu_join();
+	/* Terminate dirty quota throttling */
+	if (test_dirty_quota_increment)
+		set_dirty_quota(vm, 0);
 	pthread_join(vcpu_thread, NULL);
 
 	pr_info("Total bits checked: dirty (%"PRIu64"), clear (%"PRIu64"), "
@@ -824,6 +848,8 @@ static void help(char *name)
 	printf(" -c: specify dirty ring size, in number of entries\n");
 	printf("     (only useful for dirty-ring test; default: %"PRIu32")\n",
 	       TEST_DIRTY_RING_COUNT);
+	printf(" -q: specify incemental dirty quota (default: %"PRIu32")\n",
+	       TEST_DIRTY_QUOTA_INCREMENT);
 	printf(" -i: specify iteration counts (default: %"PRIu64")\n",
 	       TEST_HOST_LOOP_N);
 	printf(" -I: specify interval in ms (default: %"PRIu64" ms)\n",
@@ -852,11 +878,14 @@ int main(int argc, char *argv[])
 
 	guest_modes_append_default();
 
-	while ((opt = getopt(argc, argv, "c:hi:I:p:m:M:")) != -1) {
+	while ((opt = getopt(argc, argv, "c:q:hi:I:p:m:M:")) != -1) {
 		switch (opt) {
 		case 'c':
 			test_dirty_ring_count = strtol(optarg, NULL, 10);
 			break;
+		case 'q':
+			test_dirty_quota_increment = strtol(optarg, NULL, 10);
+			break;
 		case 'i':
 			p.iterations = strtol(optarg, NULL, 10);
 			break;
diff --git a/tools/testing/selftests/kvm/include/kvm_util_base.h b/tools/testing/selftests/kvm/include/kvm_util_base.h
index 24fde97f6121..68be66b9ac67 100644
--- a/tools/testing/selftests/kvm/include/kvm_util_base.h
+++ b/tools/testing/selftests/kvm/include/kvm_util_base.h
@@ -834,4 +834,8 @@ static inline int __vm_disable_nx_huge_pages(struct kvm_vm *vm)
 	return __vm_enable_cap(vm, KVM_CAP_VM_DISABLE_NX_HUGE_PAGES, 0);
 }
 
+void vcpu_set_dirty_quota(struct kvm_run *run, uint64_t dirty_quota);
+void vcpu_handle_dirty_quota_exit(struct kvm_run *run,
+			uint64_t test_dirty_quota_increment);
+
 #endif /* SELFTEST_KVM_UTIL_BASE_H */
diff --git a/tools/testing/selftests/kvm/lib/kvm_util.c b/tools/testing/selftests/kvm/lib/kvm_util.c
index 9889fe0d8919..4c7bd9807d0b 100644
--- a/tools/testing/selftests/kvm/lib/kvm_util.c
+++ b/tools/testing/selftests/kvm/lib/kvm_util.c
@@ -18,6 +18,7 @@
 #include <linux/kernel.h>
 
 #define KVM_UTIL_MIN_PFN	2
+#define PML_BUFFER_SIZE	512
 
 static int vcpu_mmap_sz(void);
 
@@ -1703,6 +1704,7 @@ static struct exit_reason {
 	{KVM_EXIT_X86_RDMSR, "RDMSR"},
 	{KVM_EXIT_X86_WRMSR, "WRMSR"},
 	{KVM_EXIT_XEN, "XEN"},
+	{KVM_EXIT_DIRTY_QUOTA_EXHAUSTED, "DIRTY_QUOTA_EXHAUSTED"},
 #ifdef KVM_EXIT_MEMORY_NOT_PRESENT
 	{KVM_EXIT_MEMORY_NOT_PRESENT, "MEMORY_NOT_PRESENT"},
 #endif
@@ -1979,3 +1981,37 @@ void __vm_get_stat(struct kvm_vm *vm, const char *stat_name, uint64_t *data,
 		break;
 	}
 }
+
+void vcpu_set_dirty_quota(struct kvm_run *run, uint64_t dirty_quota)
+{
+	run->dirty_quota = dirty_quota;
+
+	if (dirty_quota)
+		pr_info("Dirty quota throttling enabled with initial quota %"PRIu64"\n",
+			dirty_quota);
+	else
+		pr_info("Dirty quota throttling disabled\n");
+}
+
+void vcpu_handle_dirty_quota_exit(struct kvm_run *run,
+			uint64_t test_dirty_quota_increment)
+{
+	uint64_t quota = run->dirty_quota_exit.quota;
+	uint64_t count = run->dirty_quota_exit.count;
+
+	/*
+	 * Due to PML, number of pages dirtied by the vcpu can exceed its dirty
+	 * quota by PML buffer size.
+	 */
+	TEST_ASSERT(count <= quota + PML_BUFFER_SIZE, "Invalid number of pages
+		dirtied: count=%"PRIu64", quota=%"PRIu64"\n", count, quota);
+
+	TEST_ASSERT(count >= quota, "Dirty quota exit happened with quota yet to
+		be exhausted: count=%"PRIu64", quota=%"PRIu64"\n", count, quota);
+
+	if (count > quota)
+		pr_info("Dirty quota exit with unequal quota and count:
+			count=%"PRIu64", quota=%"PRIu64"\n", count, quota);
+
+	run->dirty_quota = count + test_dirty_quota_increment;
+}
-- 
2.22.3

Re: [PATCH v5 0/5] KVM: Dirty quota-based throttling

[Shivam Kumar]

Sorry for the delay. I was out sick for long.

On 12/09/22 9:39 am, Shivam Kumar wrote:
> This is v5 of the dirty quota series, with the following changes over v4:
> 
> 1. x86-specific changes separated into a new commit.
> 2. KVM requests used to handle dirty quota exit conditions.
> 
> v1:
> https://lore.kernel.org/kvm/20211114145721.209219-1-shivam.kumar1@nutanix.com/
> v2: https://lore.kernel.org/kvm/Ydx2EW6U3fpJoJF0@google.com/T/
> v3: https://lore.kernel.org/kvm/YkT1kzWidaRFdQQh@google.com/T/
> v4:
> https://lore.kernel.org/all/20220521202937.184189-1-shivam.kumar1@nutanix.com/
> 
> Thanks,
> Shivam
> 
> Shivam Kumar (5):
>    KVM: Implement dirty quota-based throttling of vcpus
>    KVM: x86: Dirty quota-based throttling of vcpus
>    KVM: arm64: Dirty quota-based throttling of vcpus
>    KVM: s390x: Dirty quota-based throttling of vcpus
>    KVM: selftests: Add selftests for dirty quota throttling
> 
>   Documentation/virt/kvm/api.rst                | 32 +++++++++++++++++
>   arch/arm64/kvm/arm.c                          |  9 +++++
>   arch/s390/kvm/kvm-s390.c                      |  9 +++++
>   arch/x86/kvm/mmu/spte.c                       |  4 +--
>   arch/x86/kvm/vmx/vmx.c                        |  3 ++
>   arch/x86/kvm/x86.c                            |  9 +++++
>   include/linux/kvm_host.h                      | 20 ++++++++++-
>   include/linux/kvm_types.h                     |  1 +
>   include/uapi/linux/kvm.h                      | 12 +++++++
>   tools/testing/selftests/kvm/dirty_log_test.c  | 33 +++++++++++++++--
>   .../selftests/kvm/include/kvm_util_base.h     |  4 +++
>   tools/testing/selftests/kvm/lib/kvm_util.c    | 36 +++++++++++++++++++
>   virt/kvm/kvm_main.c                           | 26 ++++++++++++--
>   13 files changed, 190 insertions(+), 8 deletions(-)
>