Re: [PATCH] KVM: ppc64: Enable ring-based dirty memory tracking

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On 8/6/23 10:34 pm, Kautuk Consul wrote:

Need at least a little context in the commit message itself:

"Enable ring-based dirty memory tracking on ppc64:"

- Enable CONFIG_HAVE_KVM_DIRTY_RING_ACQ_REL as ppc64 is weakly
   ordered.
- Enable CONFIG_NEED_KVM_DIRTY_RING_WITH_BITMAP because the
   kvmppc_xive_native_set_attr is called in the context of an ioctl
   syscall and will call kvmppc_xive_native_eq_sync for setting the
   KVM_DEV_XIVE_EQ_SYNC attribute which will call mark_dirty_page()
   when there isn't a running vcpu. Implemented the
   kvm_arch_allow_write_without_running_vcpu to always return true
   to allow mark_page_dirty_in_slot to mark the page dirty in the
   memslot->dirty_bitmap in this case.

Should kvm_arch_allow_write_without_running_vcpu() only return true in the context of kvmppc_xive_native_eq_sync()?

- Set KVM_DIRTY_LOG_PAGE_OFFSET for the ring buffer's physical page
   offset.
- Implement the kvm_arch_mmu_enable_log_dirty_pt_masked function required
   for the generic KVM code to call.
- Add a check to kvmppc_vcpu_run_hv for checking whether the dirty
   ring is soft full.
- Implement the kvm_arch_flush_remote_tlbs_memslot function to support
   the CONFIG_KVM_GENERIC_DIRTYLOG_READ_PROTECT config option.

On testing with live migration it was found that there is around
150-180 ms improvment in overall migration time with this

Signed-off-by: Kautuk Consul <kconsul@xxxxxxxxxxxxxxxxxx>
---
  Documentation/virt/kvm/api.rst      |  2 +-
  arch/powerpc/include/uapi/asm/kvm.h |  2 ++
  arch/powerpc/kvm/Kconfig            |  2 ++
  arch/powerpc/kvm/book3s_64_mmu_hv.c | 42 +++++++++++++++++++++++++++++
  arch/powerpc/kvm/book3s_hv.c        |  3 +++
  include/linux/kvm_dirty_ring.h      |  5 ++++
  6 files changed, 55 insertions(+), 1 deletion(-)

diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst
index add067793b90..ce1ebc513bae 100644
--- a/Documentation/virt/kvm/api.rst
+++ b/Documentation/virt/kvm/api.rst
@@ -8114,7 +8114,7 @@ regardless of what has actually been exposed through the CPUID leaf.
  8.29 KVM_CAP_DIRTY_LOG_RING/KVM_CAP_DIRTY_LOG_RING_ACQ_REL
  ----------------------------------------------------------
-:Architectures: x86, arm64
+:Architectures: x86, arm64, ppc64
  :Parameters: args[0] - size of the dirty log ring
KVM is capable of tracking dirty memory using ring buffers that are
diff --git a/arch/powerpc/include/uapi/asm/kvm.h b/arch/powerpc/include/uapi/asm/kvm.h
index 9f18fa090f1f..f722309ed7fb 100644
--- a/arch/powerpc/include/uapi/asm/kvm.h
+++ b/arch/powerpc/include/uapi/asm/kvm.h
@@ -33,6 +33,8 @@
  /* Not always available, but if it is, this is the correct offset.  */
  #define KVM_COALESCED_MMIO_PAGE_OFFSET 1
+#define KVM_DIRTY_LOG_PAGE_OFFSET 64
+
  struct kvm_regs {
  	__u64 pc;
  	__u64 cr;
diff --git a/arch/powerpc/kvm/Kconfig b/arch/powerpc/kvm/Kconfig
index 902611954200..c93354ec3bd5 100644
--- a/arch/powerpc/kvm/Kconfig
+++ b/arch/powerpc/kvm/Kconfig
@@ -26,6 +26,8 @@ config KVM
  	select IRQ_BYPASS_MANAGER
  	select HAVE_KVM_IRQ_BYPASS
  	select INTERVAL_TREE
+	select HAVE_KVM_DIRTY_RING_ACQ_REL
+	select NEED_KVM_DIRTY_RING_WITH_BITMAP
config KVM_BOOK3S_HANDLER
  	bool
diff --git a/arch/powerpc/kvm/book3s_64_mmu_hv.c b/arch/powerpc/kvm/book3s_64_mmu_hv.c
index 7f765d5ad436..c92e8022e017 100644
--- a/arch/powerpc/kvm/book3s_64_mmu_hv.c
+++ b/arch/powerpc/kvm/book3s_64_mmu_hv.c
@@ -2147,3 +2147,45 @@ void kvmppc_mmu_book3s_hv_init(struct kvm_vcpu *vcpu)
vcpu->arch.hflags |= BOOK3S_HFLAG_SLB;
  }
+
+/*
+ * kvm_arch_mmu_enable_log_dirty_pt_masked - enable dirty logging for selected
+ * dirty pages.
+ *
+ * It write protects selected pages to enable dirty logging for them.
+ */
+void kvm_arch_mmu_enable_log_dirty_pt_masked(struct kvm *kvm,
+					     struct kvm_memory_slot *slot,
+					     gfn_t gfn_offset,
+					     unsigned long mask)
+{
+	phys_addr_t base_gfn = slot->base_gfn + gfn_offset;
+	phys_addr_t start = (base_gfn +  __ffs(mask)) << PAGE_SHIFT;
+	phys_addr_t end = (base_gfn + __fls(mask) + 1) << PAGE_SHIFT;
+
+	while (start < end) {
+		pte_t *ptep;
+		unsigned int shift;
+
+		ptep = find_kvm_secondary_pte(kvm, start, &shift);
+
+		*ptep = __pte(pte_val(*ptep) & ~(_PAGE_WRITE));
On rpt I think you'd need to use kvmppc_radix_update_pte()?

+
+		start += PAGE_SIZE > +	}
+}
+
+#ifdef CONFIG_NEED_KVM_DIRTY_RING_WITH_BITMAP
+bool kvm_arch_allow_write_without_running_vcpu(struct kvm *kvm)
+{
+	return true;
+}
+#endif
+
+#ifdef CONFIG_KVM_GENERIC_DIRTYLOG_READ_PROTECT
+void kvm_arch_flush_remote_tlbs_memslot(struct kvm *kvm,
+					const struct kvm_memory_slot *memslot)
+{
+	kvm_flush_remote_tlbs(kvm);
+}
+#endif
diff --git a/arch/powerpc/kvm/book3s_hv.c b/arch/powerpc/kvm/book3s_hv.c
index 130bafdb1430..1d1264ea72c4 100644
--- a/arch/powerpc/kvm/book3s_hv.c
+++ b/arch/powerpc/kvm/book3s_hv.c
@@ -4804,6 +4804,9 @@ static int kvmppc_vcpu_run_hv(struct kvm_vcpu *vcpu)
  		return -EINTR;
  	}
+ if (kvm_dirty_ring_check_request(vcpu))
+		return 0;
+
  #ifdef CONFIG_PPC_TRANSACTIONAL_MEM
  	/*
  	 * Don't allow entry with a suspended transaction, because
diff --git a/include/linux/kvm_dirty_ring.h b/include/linux/kvm_dirty_ring.h
index 4862c98d80d3..a00301059da5 100644
--- a/include/linux/kvm_dirty_ring.h
+++ b/include/linux/kvm_dirty_ring.h
@@ -69,6 +69,11 @@ static inline void kvm_dirty_ring_free(struct kvm_dirty_ring *ring)
  {
  }
+static inline bool kvm_dirty_ring_check_request(struct kvm_vcpu *vcpu)
+{
+	return false;
+}
+ >   #else /* CONFIG_HAVE_KVM_DIRTY_RING */
int kvm_cpu_dirty_log_size(void);




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