[PATCH v3 02/34] KVM: x86: hyper-v: Introduce TLB flush ring

Vitaly Kuznetsov
2022-04-14T13:39:25Z

To allow flushing individual GVAs instead of always flushing the whole
VPID a per-vCPU structure to pass the requests is needed. Introduce a
simple ring write-locked structure to hold two types of entries:
individual GVA (GFN + up to 4095 following GFNs in the lower 12 bits)
and 'flush all'.

The queuing rule is: if there's not enough space on the ring to put
the request and leave at least 1 entry for 'flush all' - put 'flush
all' entry.

The size of the ring is arbitrary set to '16'.

Note, kvm_hv_flush_tlb() only queues 'flush all' entries for now so
there's very small functional change but the infrastructure is
prepared to handle individual GVA flush requests.

Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
---
arch/x86/include/asm/kvm_host.h | 16 +++++++
arch/x86/kvm/hyperv.c | 83 +++++++++++++++++++++++++++++++++
arch/x86/kvm/hyperv.h | 13 ++++++
arch/x86/kvm/x86.c | 5 +-
arch/x86/kvm/x86.h | 1 +
5 files changed, 116 insertions(+), 2 deletions(-)

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index 1de3ad9308d8..b4dd2ff61658 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -578,6 +578,20 @@ struct kvm_vcpu_hv_synic {
bool dont_zero_synic_pages;
};

+#define KVM_HV_TLB_FLUSH_RING_SIZE (16)
+
+struct kvm_vcpu_hv_tlb_flush_entry {
+ u64 addr;
+ u64 flush_all:1;
+ u64 pad:63;
+};
+
+struct kvm_vcpu_hv_tlb_flush_ring {
+ int read_idx, write_idx;
+ spinlock_t write_lock;
+ struct kvm_vcpu_hv_tlb_flush_entry entries[KVM_HV_TLB_FLUSH_RING_SIZE];
+};
+
/* Hyper-V per vcpu emulation context */
struct kvm_vcpu_hv {
struct kvm_vcpu *vcpu;
@@ -597,6 +611,8 @@ struct kvm_vcpu_hv {
u32 enlightenments_ebx; /* HYPERV_CPUID_ENLIGHTMENT_INFO.EBX */
u32 syndbg_cap_eax; /* HYPERV_CPUID_SYNDBG_PLATFORM_CAPABILITIES.EAX */
} cpuid_cache;
+
+ struct kvm_vcpu_hv_tlb_flush_ring tlb_flush_ring;
};

/* Xen HVM per vcpu emulation context */
diff --git a/arch/x86/kvm/hyperv.c b/arch/x86/kvm/hyperv.c
index b402ad059eb9..fb716cf919ed 100644
--- a/arch/x86/kvm/hyperv.c
+++ b/arch/x86/kvm/hyperv.c
@@ -29,6 +29,7 @@
#include <linux/kvm_host.h>
#include <linux/highmem.h>
#include <linux/sched/cputime.h>
+#include <linux/spinlock.h>
#include <linux/eventfd.h>

#include <asm/apicdef.h>
@@ -954,6 +955,8 @@ static int kvm_hv_vcpu_init(struct kvm_vcpu *vcpu)

hv_vcpu->vp_index = vcpu->vcpu_idx;

+ spin_lock_init(&hv_vcpu->tlb_flush_ring.write_lock);
+
return 0;
}

@@ -1789,6 +1792,74 @@ static u64 kvm_get_sparse_vp_set(struct kvm *kvm, struct kvm_hv_hcall *hc,
var_cnt * sizeof(*sparse_banks));
}

+static inline int hv_tlb_flush_ring_free(struct kvm_vcpu_hv *hv_vcpu,
+ int read_idx, int write_idx)
+{
+ if (write_idx >= read_idx)
+ return KVM_HV_TLB_FLUSH_RING_SIZE - (write_idx - read_idx) - 1;
+
+ return read_idx - write_idx - 1;
+}
+
+static void hv_tlb_flush_ring_enqueue(struct kvm_vcpu *vcpu)
+{
+ struct kvm_vcpu_hv_tlb_flush_ring *tlb_flush_ring;
+ struct kvm_vcpu_hv *hv_vcpu = to_hv_vcpu(vcpu);
+ int ring_free, write_idx, read_idx;
+ unsigned long flags;
+
+ if (!hv_vcpu)
+ return;
+
+ tlb_flush_ring = &hv_vcpu->tlb_flush_ring;
+
+ spin_lock_irqsave(&tlb_flush_ring->write_lock, flags);
+
+ /*
+ * 'read_idx' is updated by the vCPU which does the flush, this
+ * happens without 'tlb_flush_ring->write_lock' being held; make
+ * sure we read it once.
+ */
+ read_idx = READ_ONCE(tlb_flush_ring->read_idx);
+ /*
+ * 'write_idx' is only updated here, under 'tlb_flush_ring->write_lock'.
+ * allow the compiler to re-read it, it can't change.
+ */
+ write_idx = tlb_flush_ring->write_idx;
+
+ ring_free = hv_tlb_flush_ring_free(hv_vcpu, read_idx, write_idx);
+ /* Full ring always contains 'flush all' entry */
+ if (!ring_free)
+ goto out_unlock;
+
+ tlb_flush_ring->entries[write_idx].addr = 0;
+ tlb_flush_ring->entries[write_idx].flush_all = 1;
+ /*
+ * Advance write index only after filling in the entry to
+ * synchronize with lockless reader.
+ */
+ smp_wmb();
+ tlb_flush_ring->write_idx = (write_idx + 1) % KVM_HV_TLB_FLUSH_RING_SIZE;
+
+out_unlock:
+ spin_unlock_irqrestore(&tlb_flush_ring->write_lock, flags);
+}
+
+void kvm_hv_vcpu_flush_tlb(struct kvm_vcpu *vcpu)
+{
+ struct kvm_vcpu_hv_tlb_flush_ring *tlb_flush_ring;
+ struct kvm_vcpu_hv *hv_vcpu = to_hv_vcpu(vcpu);
+
+ kvm_vcpu_flush_tlb_guest(vcpu);
+
+ if (!hv_vcpu)
+ return;
+
+ tlb_flush_ring = &hv_vcpu->tlb_flush_ring;
+
+ tlb_flush_ring->read_idx = tlb_flush_ring->write_idx;
+}
+
static u64 kvm_hv_flush_tlb(struct kvm_vcpu *vcpu, struct kvm_hv_hcall *hc)
{
struct kvm *kvm = vcpu->kvm;
@@ -1797,6 +1868,8 @@ static u64 kvm_hv_flush_tlb(struct kvm_vcpu *vcpu, struct kvm_hv_hcall *hc)
DECLARE_BITMAP(vcpu_mask, KVM_MAX_VCPUS);
u64 valid_bank_mask;
u64 sparse_banks[KVM_HV_MAX_SPARSE_VCPU_SET_BITS];
+ struct kvm_vcpu *v;
+ unsigned long i;
bool all_cpus;

/*
@@ -1876,10 +1949,20 @@ static u64 kvm_hv_flush_tlb(struct kvm_vcpu *vcpu, struct kvm_hv_hcall *hc)
* analyze it here, flush TLB regardless of the specified address space.
*/
if (all_cpus) {
+ kvm_for_each_vcpu(i, v, kvm)
+ hv_tlb_flush_ring_enqueue(v);
+
kvm_make_all_cpus_request(kvm, KVM_REQ_HV_TLB_FLUSH);
} else {
sparse_set_to_vcpu_mask(kvm, sparse_banks, valid_bank_mask, vcpu_mask);

+ for_each_set_bit(i, vcpu_mask, KVM_MAX_VCPUS) {
+ v = kvm_get_vcpu(kvm, i);
+ if (!v)
+ continue;
+ hv_tlb_flush_ring_enqueue(v);
+ }
+
kvm_make_vcpus_request_mask(kvm, KVM_REQ_HV_TLB_FLUSH, vcpu_mask);
}

diff --git a/arch/x86/kvm/hyperv.h b/arch/x86/kvm/hyperv.h
index da2737f2a956..6847caeaaf84 100644
--- a/arch/x86/kvm/hyperv.h
+++ b/arch/x86/kvm/hyperv.h
@@ -147,4 +147,17 @@ int kvm_vm_ioctl_hv_eventfd(struct kvm *kvm, struct kvm_hyperv_eventfd *args);
int kvm_get_hv_cpuid(struct kvm_vcpu *vcpu, struct kvm_cpuid2 *cpuid,
struct kvm_cpuid_entry2 __user *entries);

+
+static inline void kvm_hv_vcpu_empty_flush_tlb(struct kvm_vcpu *vcpu)
+{
+ struct kvm_vcpu_hv *hv_vcpu = to_hv_vcpu(vcpu);
+
+ if (!hv_vcpu)
+ return;
+
+ hv_vcpu->tlb_flush_ring.read_idx = hv_vcpu->tlb_flush_ring.write_idx;
+}
+void kvm_hv_vcpu_flush_tlb(struct kvm_vcpu *vcpu);
+
+
#endif
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index f633cff8cd7f..e5aec386d299 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -3324,7 +3324,7 @@ static void kvm_vcpu_flush_tlb_all(struct kvm_vcpu *vcpu)
static_call(kvm_x86_flush_tlb_all)(vcpu);
}

-static void kvm_vcpu_flush_tlb_guest(struct kvm_vcpu *vcpu)
+void kvm_vcpu_flush_tlb_guest(struct kvm_vcpu *vcpu)
{
++vcpu->stat.tlb_flush;

@@ -3362,7 +3362,8 @@ void kvm_service_local_tlb_flush_requests(struct kvm_vcpu *vcpu)

if (kvm_check_request(KVM_REQ_TLB_FLUSH_GUEST, vcpu)) {
kvm_vcpu_flush_tlb_guest(vcpu);
- kvm_clear_request(KVM_REQ_HV_TLB_FLUSH, vcpu);
+ if (kvm_check_request(KVM_REQ_HV_TLB_FLUSH, vcpu))
+ kvm_hv_vcpu_empty_flush_tlb(vcpu);
} else if (kvm_check_request(KVM_REQ_HV_TLB_FLUSH, vcpu)) {
kvm_vcpu_flush_tlb_guest(vcpu);
}
diff --git a/arch/x86/kvm/x86.h b/arch/x86/kvm/x86.h
index 588792f00334..2324f496c500 100644
--- a/arch/x86/kvm/x86.h
+++ b/arch/x86/kvm/x86.h
@@ -58,6 +58,7 @@ static inline unsigned int __shrink_ple_window(unsigned int val,

#define MSR_IA32_CR_PAT_DEFAULT 0x0007040600070406ULL

+void kvm_vcpu_flush_tlb_guest(struct kvm_vcpu *vcpu);
void kvm_service_local_tlb_flush_requests(struct kvm_vcpu *vcpu);
int kvm_check_nested_events(struct kvm_vcpu *vcpu);

--
2.35.1