[PATCH v3 04/34] KVM: x86: hyper-v: Handle HVCALL_FLUSH_VIRTUAL_ADDRESS_LIST{,EX} calls gently

[Vitaly Kuznetsov <vkuznets@redhat.com>]

Currently, HVCALL_FLUSH_VIRTUAL_ADDRESS_LIST{,EX} calls are handled
the exact same way as HVCALL_FLUSH_VIRTUAL_ADDRESS_SPACE{,EX}: by
flushing the whole VPID and this is sub-optimal. Switch to handling
these requests with 'flush_tlb_gva()' hooks instead. Use the newly
introduced TLB flush ring to queue the requests.

Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
---
 arch/x86/kvm/hyperv.c | 132 ++++++++++++++++++++++++++++++++++++------
 1 file changed, 115 insertions(+), 17 deletions(-)

diff --git a/arch/x86/kvm/hyperv.c b/arch/x86/kvm/hyperv.c
index d66c27fd1e8a..759e1a16e5c3 100644
--- a/arch/x86/kvm/hyperv.c
+++ b/arch/x86/kvm/hyperv.c
@@ -1805,6 +1805,13 @@ static u64 kvm_get_sparse_vp_set(struct kvm *kvm, struct kvm_hv_hcall *hc,
 				  sparse_banks, consumed_xmm_halves, offset);
 }
 
+static int kvm_hv_get_tlb_flush_entries(struct kvm *kvm, struct kvm_hv_hcall *hc, u64 entries[],
+				       int consumed_xmm_halves, gpa_t offset)
+{
+	return kvm_hv_get_hc_data(kvm, hc, hc->rep_cnt, hc->rep_cnt,
+				  entries, consumed_xmm_halves, offset);
+}
+
 static inline int hv_tlb_flush_ring_free(struct kvm_vcpu_hv *hv_vcpu,
 					 int read_idx, int write_idx)
 {
@@ -1814,12 +1821,13 @@ static inline int hv_tlb_flush_ring_free(struct kvm_vcpu_hv *hv_vcpu,
 	return read_idx - write_idx - 1;
 }
 
-static void hv_tlb_flush_ring_enqueue(struct kvm_vcpu *vcpu)
+static void hv_tlb_flush_ring_enqueue(struct kvm_vcpu *vcpu, u64 *entries, int count)
 {
 	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;
+	int i;
 
 	if (!hv_vcpu)
 		return;
@@ -1845,14 +1853,34 @@ static void hv_tlb_flush_ring_enqueue(struct kvm_vcpu *vcpu)
 	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.
+	 * All entries should fit on the ring leaving one free for 'flush all'
+	 * entry in case another request comes in. In case there's not enough
+	 * space, just put 'flush all' entry there.
+	 */
+	if (!count || count >= ring_free - 1 || !entries) {
+		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;
+		goto out_unlock;
+	}
+
+	for (i = 0; i < count; i++) {
+		tlb_flush_ring->entries[write_idx].addr = entries[i];
+		tlb_flush_ring->entries[write_idx].flush_all = 0;
+		write_idx = (write_idx + 1) % KVM_HV_TLB_FLUSH_RING_SIZE;
+	}
+	/*
+	 * 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;
+	tlb_flush_ring->write_idx = write_idx;
 
 out_unlock:
 	spin_unlock_irqrestore(&tlb_flush_ring->write_lock, flags);
@@ -1862,15 +1890,58 @@ 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);
+	struct kvm_vcpu_hv_tlb_flush_entry *entry;
+	int read_idx, write_idx;
+	u64 address;
+	u32 count;
+	int i, j;
 
-	kvm_vcpu_flush_tlb_guest(vcpu);
-
-	if (!hv_vcpu)
+	if (!tdp_enabled || !hv_vcpu) {
+		kvm_vcpu_flush_tlb_guest(vcpu);
 		return;
+	}
 
 	tlb_flush_ring = &hv_vcpu->tlb_flush_ring;
 
-	tlb_flush_ring->read_idx = tlb_flush_ring->write_idx;
+	/*
+	 * TLB flush must be performed on the target vCPU so 'read_idx'
+	 * (AKA 'tail') cannot change underneath, the compiler is free
+	 * to re-read it.
+	 */
+	read_idx = tlb_flush_ring->read_idx;
+
+	/*
+	 * 'write_idx' (AKA 'head') can be concurently updated by a different
+	 * vCPU so we must be sure it's read once.
+	 */
+	write_idx = READ_ONCE(tlb_flush_ring->write_idx);
+
+	/* Pairs with smp_wmb() in hv_tlb_flush_ring_enqueue() */
+	smp_rmb();
+
+	for (i = read_idx; i != write_idx; i = (i + 1) % KVM_HV_TLB_FLUSH_RING_SIZE) {
+		entry = &tlb_flush_ring->entries[i];
+
+		if (entry->flush_all)
+			goto out_flush_all;
+
+		/*
+		 * Lower 12 bits of 'address' encode the number of additional
+		 * pages to flush.
+		 */
+		address = entry->addr & PAGE_MASK;
+		count = (entry->addr & ~PAGE_MASK) + 1;
+		for (j = 0; j < count; j++)
+			static_call(kvm_x86_flush_tlb_gva)(vcpu, address + j * PAGE_SIZE);
+	}
+	++vcpu->stat.tlb_flush;
+	goto out_empty_ring;
+
+out_flush_all:
+	kvm_vcpu_flush_tlb_guest(vcpu);
+
+out_empty_ring:
+	tlb_flush_ring->read_idx = write_idx;
 }
 
 static u64 kvm_hv_flush_tlb(struct kvm_vcpu *vcpu, struct kvm_hv_hcall *hc)
@@ -1879,11 +1950,22 @@ static u64 kvm_hv_flush_tlb(struct kvm_vcpu *vcpu, struct kvm_hv_hcall *hc)
 	struct hv_tlb_flush_ex flush_ex;
 	struct hv_tlb_flush flush;
 	DECLARE_BITMAP(vcpu_mask, KVM_MAX_VCPUS);
+	/*
+	 * Normally, there can be no more than 'KVM_HV_TLB_FLUSH_RING_SIZE - 1'
+	 * entries on the TLB Flush ring as when 'read_idx == write_idx' the
+	 * ring is considered as empty. The last entry on the ring, however,
+	 * needs to be always left free for 'flush all' entry which gets placed
+	 * when there is not enough space to put all the requested entries.
+	 */
+	u64 __tlb_flush_entries[KVM_HV_TLB_FLUSH_RING_SIZE - 2];
+	u64 *tlb_flush_entries;
 	u64 valid_bank_mask;
 	u64 sparse_banks[KVM_HV_MAX_SPARSE_VCPU_SET_BITS];
 	struct kvm_vcpu *v;
 	unsigned long i;
 	bool all_cpus;
+	int consumed_xmm_halves = 0;
+	gpa_t data_offset;
 
 	/*
 	 * The Hyper-V TLFS doesn't allow more than 64 sparse banks, e.g. the
@@ -1899,10 +1981,12 @@ static u64 kvm_hv_flush_tlb(struct kvm_vcpu *vcpu, struct kvm_hv_hcall *hc)
 			flush.address_space = hc->ingpa;
 			flush.flags = hc->outgpa;
 			flush.processor_mask = sse128_lo(hc->xmm[0]);
+			consumed_xmm_halves = 1;
 		} else {
 			if (unlikely(kvm_read_guest(kvm, hc->ingpa,
 						    &flush, sizeof(flush))))
 				return HV_STATUS_INVALID_HYPERCALL_INPUT;
+			data_offset = sizeof(flush);
 		}
 
 		trace_kvm_hv_flush_tlb(flush.processor_mask,
@@ -1926,10 +2010,12 @@ static u64 kvm_hv_flush_tlb(struct kvm_vcpu *vcpu, struct kvm_hv_hcall *hc)
 			flush_ex.flags = hc->outgpa;
 			memcpy(&flush_ex.hv_vp_set,
 			       &hc->xmm[0], sizeof(hc->xmm[0]));
+			consumed_xmm_halves = 2;
 		} else {
 			if (unlikely(kvm_read_guest(kvm, hc->ingpa, &flush_ex,
 						    sizeof(flush_ex))))
 				return HV_STATUS_INVALID_HYPERCALL_INPUT;
+			data_offset = sizeof(flush_ex);
 		}
 
 		trace_kvm_hv_flush_tlb_ex(flush_ex.hv_vp_set.valid_bank_mask,
@@ -1945,25 +2031,37 @@ static u64 kvm_hv_flush_tlb(struct kvm_vcpu *vcpu, struct kvm_hv_hcall *hc)
 			return HV_STATUS_INVALID_HYPERCALL_INPUT;
 
 		if (all_cpus)
-			goto do_flush;
+			goto read_flush_entries;
 
 		if (!hc->var_cnt)
 			goto ret_success;
 
-		if (kvm_get_sparse_vp_set(kvm, hc, sparse_banks, 2,
-					  offsetof(struct hv_tlb_flush_ex,
-						   hv_vp_set.bank_contents)))
+		if (kvm_get_sparse_vp_set(kvm, hc, sparse_banks, consumed_xmm_halves,
+					  data_offset))
+			return HV_STATUS_INVALID_HYPERCALL_INPUT;
+		data_offset += hc->var_cnt * sizeof(sparse_banks[0]);
+		consumed_xmm_halves += hc->var_cnt;
+	}
+
+read_flush_entries:
+	if (hc->code == HVCALL_FLUSH_VIRTUAL_ADDRESS_SPACE ||
+	    hc->code == HVCALL_FLUSH_VIRTUAL_ADDRESS_SPACE_EX ||
+	    hc->rep_cnt > ARRAY_SIZE(__tlb_flush_entries)) {
+		tlb_flush_entries = NULL;
+	} else {
+		if (kvm_hv_get_tlb_flush_entries(kvm, hc, __tlb_flush_entries,
+						consumed_xmm_halves, data_offset))
 			return HV_STATUS_INVALID_HYPERCALL_INPUT;
+		tlb_flush_entries = __tlb_flush_entries;
 	}
 
-do_flush:
 	/*
 	 * vcpu->arch.cr3 may not be up-to-date for running vCPUs so we can't
 	 * 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);
+			hv_tlb_flush_ring_enqueue(v, tlb_flush_entries, hc->rep_cnt);
 
 		kvm_make_all_cpus_request(kvm, KVM_REQ_HV_TLB_FLUSH);
 	} else {
@@ -1973,7 +2071,7 @@ static u64 kvm_hv_flush_tlb(struct kvm_vcpu *vcpu, struct kvm_hv_hcall *hc)
 			v = kvm_get_vcpu(kvm, i);
 			if (!v)
 				continue;
-			hv_tlb_flush_ring_enqueue(v);
+			hv_tlb_flush_ring_enqueue(v, tlb_flush_entries, hc->rep_cnt);
 		}
 
 		kvm_make_vcpus_request_mask(kvm, KVM_REQ_HV_TLB_FLUSH, vcpu_mask);
-- 
2.35.1