Re: [PATCH v4 03/15] KVM: async_pf: Make GFN slot management generic

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Hi Eric,

On 11/11/21 1:00 AM, Eric Auger wrote:
On 8/15/21 2:59 AM, Gavin Shan wrote:
It's not allowed to fire duplicate notification for same GFN on
x86 platform, with help of a hash table. This mechanism is going
s/, with help of a hash table/this is achieved through a hash table
to be used by arm64 and this makes the code generic and shareable
s/and this makes/.\n Turn the code generic
by multiple platforms.

    * As this mechanism isn't needed by all platforms, a new kernel
      config option (CONFIG_ASYNC_PF_SLOT) is introduced so that it
      can be disabled at compiling time.
compile time

Ok.


    * The code is basically copied from x86 platform and the functions
      are renamed to reflect the fact: (a) the input parameters are
      vCPU and GFN.
not for reset
(b) The operations are resetting, searching, adding

Ok.

      and removing.
find, add, remove ops are renamed with _slot suffix

Ok. The commit log will be improved based on your suggestions in
next respin :)


    * Helper stub is also added on !CONFIG_KVM_ASYNC_PF because we're
      going to use IS_ENABLED() instead of #ifdef on arm64 when the
      asynchronous page fault is supported.

This is preparatory work to use the newly introduced functions on x86
platform and arm64 in subsequent patches.

Signed-off-by: Gavin Shan <gshan@xxxxxxxxxx>
---
  include/linux/kvm_host.h | 18 +++++++++
  virt/kvm/Kconfig         |  3 ++
  virt/kvm/async_pf.c      | 85 ++++++++++++++++++++++++++++++++++++++++
  3 files changed, 106 insertions(+)

diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index a5f990f6dc35..a9685c2b2250 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -298,6 +298,9 @@ struct kvm_vcpu {
#ifdef CONFIG_KVM_ASYNC_PF
  	struct {
+#ifdef CONFIG_KVM_ASYNC_PF_SLOT
+		gfn_t gfns[ASYNC_PF_PER_VCPU];
+#endif
  		u32 queued;
  		struct list_head queue;
  		struct list_head done;
@@ -339,6 +342,13 @@ struct kvm_async_pf {
  	bool				notpresent_injected;
  };
+#ifdef CONFIG_KVM_ASYNC_PF_SLOT
+void kvm_async_pf_reset_slot(struct kvm_vcpu *vcpu);
this does not reset a "slot" but the whole hash table. So to me this
shouldn't be renamed with _slot suffix. reset_hash or reset_all_slots?

Sure, lets have kvm_async_pf_reset_all_slots() in next respin.

+void kvm_async_pf_add_slot(struct kvm_vcpu *vcpu, gfn_t gfn);
+void kvm_async_pf_remove_slot(struct kvm_vcpu *vcpu, gfn_t gfn);
+bool kvm_async_pf_find_slot(struct kvm_vcpu *vcpu, gfn_t gfn);
+#endif
+
  static inline bool kvm_check_async_pf_completion_queue(struct kvm_vcpu *vcpu)
  {
  	return !list_empty_careful(&vcpu->async_pf.done);
@@ -350,6 +360,14 @@ bool kvm_setup_async_pf(struct kvm_vcpu *vcpu, gpa_t cr2_or_gpa,
  			unsigned long hva, struct kvm_arch_async_pf *arch);
  int kvm_async_pf_wakeup_all(struct kvm_vcpu *vcpu);
  #else
+static inline void kvm_async_pf_reset_slot(struct kvm_vcpu *vcpu) { }
+static inline void kvm_async_pf_add_slot(struct kvm_vcpu *vcpu, gfn_t gfn) { }
+static inline void kvm_async_pf_remove_slot(struct kvm_vcpu *vcpu, gfn_t gfn) { }
+static inline bool kvm_async_pf_find_slot(struct kvm_vcpu *vcpu, gfn_t gfn)
+{
+	return false;
+}
+
  static inline bool kvm_check_async_pf_completion_queue(struct kvm_vcpu *vcpu)
  {
  	return false;
diff --git a/virt/kvm/Kconfig b/virt/kvm/Kconfig
index 62b39149b8c8..59b518c8c205 100644
--- a/virt/kvm/Kconfig
+++ b/virt/kvm/Kconfig
@@ -23,6 +23,9 @@ config KVM_MMIO
  config KVM_ASYNC_PF
         bool
+config KVM_ASYNC_PF_SLOT
+	bool
+
  # Toggle to switch between direct notification and batch job
  config KVM_ASYNC_PF_SYNC
         bool
diff --git a/virt/kvm/async_pf.c b/virt/kvm/async_pf.c
index d145a61a046a..0d1fdb2932af 100644
--- a/virt/kvm/async_pf.c
+++ b/virt/kvm/async_pf.c
@@ -13,12 +13,97 @@
  #include <linux/module.h>
  #include <linux/mmu_context.h>
  #include <linux/sched/mm.h>
+#ifdef CONFIG_KVM_ASYNC_PF_SLOT
+#include <linux/hash.h>
+#endif
#include "async_pf.h"
  #include <trace/events/kvm.h>
static struct kmem_cache *async_pf_cache; +#ifdef CONFIG_KVM_ASYNC_PF_SLOT
+static inline u32 kvm_async_pf_hash(gfn_t gfn)
+{
+	BUILD_BUG_ON(!is_power_of_2(ASYNC_PF_PER_VCPU));
+
+	return hash_32(gfn & 0xffffffff, order_base_2(ASYNC_PF_PER_VCPU));
+}
+
+static inline u32 kvm_async_pf_next_slot(u32 key)
+{
+	return (key + 1) & (ASYNC_PF_PER_VCPU - 1);
+}
+
+static u32 kvm_async_pf_slot(struct kvm_vcpu *vcpu, gfn_t gfn)
+{
+	u32 key = kvm_async_pf_hash(gfn);
+	int i;
+
+	for (i = 0; i < ASYNC_PF_PER_VCPU &&
+		(vcpu->async_pf.gfns[key] != gfn &&
+		vcpu->async_pf.gfns[key] != ~0); i++)
+		key = kvm_async_pf_next_slot(key);
+
+	return key;
+}
+
+void kvm_async_pf_reset_slot(struct kvm_vcpu *vcpu)
+{
+	int i;
+
+	for (i = 0; i < ASYNC_PF_PER_VCPU; i++)
+		vcpu->async_pf.gfns[i] = ~0;
+}
+
+void kvm_async_pf_add_slot(struct kvm_vcpu *vcpu, gfn_t gfn)
+{
+	u32 key = kvm_async_pf_hash(gfn);
+
+	while (vcpu->async_pf.gfns[key] != ~0)
+		key = kvm_async_pf_next_slot(key);
+
+	vcpu->async_pf.gfns[key] = gfn;
+}
+
+void kvm_async_pf_remove_slot(struct kvm_vcpu *vcpu, gfn_t gfn)
+{
+	u32 i, j, k;
+
+	i = j = kvm_async_pf_slot(vcpu, gfn);
+
+	if (WARN_ON_ONCE(vcpu->async_pf.gfns[i] != gfn))
+		return;
+
+	while (true) {
+		vcpu->async_pf.gfns[i] = ~0;
+
+		do {
+			j = kvm_async_pf_next_slot(j);
+			if (vcpu->async_pf.gfns[j] == ~0)
+				return;
+
+			k = kvm_async_pf_hash(vcpu->async_pf.gfns[j]);
+			/*
+			 * k lies cyclically in ]i,j]
+			 * |    i.k.j |
+			 * |....j i.k.| or  |.k..j i...|
+			 */
+		} while ((i <= j) ? (i < k && k <= j) : (i < k || k <= j));
+
+		vcpu->async_pf.gfns[i] = vcpu->async_pf.gfns[j];
+		i = j;
+	}
+}
+
+bool kvm_async_pf_find_slot(struct kvm_vcpu *vcpu, gfn_t gfn)
+{
+	u32 key = kvm_async_pf_slot(vcpu, gfn);
+
+	return vcpu->async_pf.gfns[key] == gfn;
+}
+#endif /* CONFIG_KVM_ASYNC_PF_SLOT */
+
  int kvm_async_pf_init(void)
  {
  	async_pf_cache = KMEM_CACHE(kvm_async_pf, 0);


Thanks,
Gavin

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