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@xxxxxxxxxxx>
Suggested-by: Manish Mishra <manish.mishra@xxxxxxxxxxx>
Co-developed-by: Anurag Madnawat <anurag.madnawat@xxxxxxxxxxx>
Signed-off-by: Anurag Madnawat <anurag.madnawat@xxxxxxxxxxx>
Signed-off-by: Shivam Kumar <shivam.kumar1@xxxxxxxxxxx>
---
Documentation/virt/kvm/api.rst | 35 ++++++++++++++++++++++++++++++++++
arch/x86/kvm/Kconfig | 1 +
include/linux/kvm_host.h | 5 ++++-
include/linux/kvm_types.h | 1 +
include/uapi/linux/kvm.h | 13 +++++++++++++
tools/include/uapi/linux/kvm.h | 1 +
virt/kvm/Kconfig | 4 ++++
virt/kvm/kvm_main.c | 25 +++++++++++++++++++++---
8 files changed, 81 insertions(+), 4 deletions(-)
diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst
index eee9f857a986..4568faa33c6d 100644
--- a/Documentation/virt/kvm/api.rst
+++ b/Documentation/virt/kvm/api.rst
@@ -6513,6 +6513,26 @@ 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://urldefense.proofpoint.com/v2/url?u=https-3A__github.com_riscv_riscv-2Dsbi-2Ddoc&d=DwIBAg&c=s883GpUCOChKOHiocYtGcg&r=4hVFP4-J13xyn-OcN0apTCh8iKZRosf5OJTQePXBMB8&m=tRXKbxC9SnS7eawp-UoL_Dqi0C8tdGVG6pmh1Gv6Ijw1OItZ-EFLCPz4aAQ_3sob&s=HFLZ0ulDwLg_-wHdDvDhunY5olDW4tZ-6NQQE9WirIY&e= .
+::
+
+ /* 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: the current count of pages dirtied by the VCPU, can be
+ skewed based on the size of the pages accessed by each vCPU.
+ quota: 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 */
@@ -6567,6 +6587,21 @@ 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 pages. If a
+hardware ring buffer is used, the overrun is bounded by the size of the buffer
+(512 entries for PML).
+
+::
};
diff --git a/arch/x86/kvm/Kconfig b/arch/x86/kvm/Kconfig
index 67be7f217e37..bdbd36321d52 100644
--- a/arch/x86/kvm/Kconfig
+++ b/arch/x86/kvm/Kconfig
@@ -48,6 +48,7 @@ config KVM
select KVM_VFIO
select SRCU
select INTERVAL_TREE
+ select HAVE_KVM_DIRTY_QUOTA
select HAVE_KVM_PM_NOTIFIER if PM
help
Support hosting fully virtualized guest machines using hardware
diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index 18592bdf4c1b..0b9b5c251a04 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -151,11 +151,12 @@ static inline bool is_error_page(struct page *page)
#define KVM_REQUEST_NO_ACTION BIT(10)
/*
* Architecture-independent vcpu->requests bit members
- * Bits 3-7 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_DIRTY_QUOTA_EXIT 4
