[PATCH v11 09/46] KVM: x86: hyper-v: Introduce TLB flush fifo

Vitaly Kuznetsov
2022-10-04T12:41:21Z

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

The size of the fifo is arbitrarily set to '16'.

Note, kvm_hv_flush_tlb() only queues 'flush all' entries for now and
kvm_hv_vcpu_flush_tlb() doesn't actually read the fifo just resets the
queue before returning -EOPNOTSUPP (which triggers full TLB flush) so
the functional change is very small 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 | 20 ++++++++++++++
arch/x86/kvm/hyperv.c | 47 +++++++++++++++++++++++++++++++++
arch/x86/kvm/hyperv.h | 15 +++++++++++
arch/x86/kvm/svm/svm.c | 2 +-
arch/x86/kvm/x86.c | 13 ++++++---
arch/x86/kvm/x86.h | 1 +
6 files changed, 94 insertions(+), 4 deletions(-)

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index 45c390c804f0..c97161436a9d 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -25,6 +25,7 @@
#include <linux/clocksource.h>
#include <linux/irqbypass.h>
#include <linux/hyperv.h>
+#include <linux/kfifo.h>

#include <asm/apic.h>
#include <asm/pvclock-abi.h>
@@ -599,6 +600,23 @@ struct kvm_vcpu_hv_synic {
bool dont_zero_synic_pages;
};

+/* The maximum number of entries on the TLB flush fifo. */
+#define KVM_HV_TLB_FLUSH_FIFO_SIZE (16)
+/*
+ * Note: the following 'magic' entry is made up by KVM to avoid putting
+ * anything besides GVA on the TLB flush fifo. It is theoretically possible
+ * to observe a request to flush 4095 PFNs starting from 0xfffffffffffff000
+ * which will look identical. KVM's action to 'flush everything' instead of
+ * flushing these particular addresses is, however, fully legitimate as
+ * flushing more than requested is always OK.
+ */
+#define KVM_HV_TLB_FLUSHALL_ENTRY ((u64)-1)
+
+struct kvm_vcpu_hv_tlb_flush_fifo {
+ spinlock_t write_lock;
+ DECLARE_KFIFO(entries, u64, KVM_HV_TLB_FLUSH_FIFO_SIZE);
+};
+
/* Hyper-V per vcpu emulation context */
struct kvm_vcpu_hv {
struct kvm_vcpu *vcpu;
@@ -620,6 +638,8 @@ struct kvm_vcpu_hv {
u32 nested_eax; /* HYPERV_CPUID_NESTED_FEATURES.EAX */
u32 nested_ebx; /* HYPERV_CPUID_NESTED_FEATURES.EBX */
} cpuid_cache;
+
+ struct kvm_vcpu_hv_tlb_flush_fifo tlb_flush_fifo;
};

/* Xen HVM per vcpu emulation context */
diff --git a/arch/x86/kvm/hyperv.c b/arch/x86/kvm/hyperv.c
index 3c0f639f6a05..9d9a5ff2d54b 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 +955,9 @@ int kvm_hv_vcpu_init(struct kvm_vcpu *vcpu)

hv_vcpu->vp_index = vcpu->vcpu_idx;

+ INIT_KFIFO(hv_vcpu->tlb_flush_fifo.entries);
+ spin_lock_init(&hv_vcpu->tlb_flush_fifo.write_lock);
+
return 0;
}

@@ -1783,6 +1787,37 @@ static u64 kvm_get_sparse_vp_set(struct kvm *kvm, struct kvm_hv_hcall *hc,
var_cnt * sizeof(*sparse_banks));
}

+static void hv_tlb_flush_enqueue(struct kvm_vcpu *vcpu)
+{
+ struct kvm_vcpu_hv_tlb_flush_fifo *tlb_flush_fifo;
+ struct kvm_vcpu_hv *hv_vcpu = to_hv_vcpu(vcpu);
+ u64 flush_all_entry = KVM_HV_TLB_FLUSHALL_ENTRY;
+
+ if (!hv_vcpu)
+ return;
+
+ tlb_flush_fifo = &hv_vcpu->tlb_flush_fifo;
+
+ kfifo_in_spinlocked_noirqsave(&tlb_flush_fifo->entries, &flush_all_entry,
+ 1, &tlb_flush_fifo->write_lock);
+}
+
+int kvm_hv_vcpu_flush_tlb(struct kvm_vcpu *vcpu)
+{
+ struct kvm_vcpu_hv_tlb_flush_fifo *tlb_flush_fifo;
+ struct kvm_vcpu_hv *hv_vcpu = to_hv_vcpu(vcpu);
+
+ if (!hv_vcpu)
+ return -EINVAL;
+
+ tlb_flush_fifo = &hv_vcpu->tlb_flush_fifo;
+
+ kfifo_reset_out(&tlb_flush_fifo->entries);
+
+ /* Precise flushing isn't implemented yet. */
+ return -EOPNOTSUPP;
+}
+
static u64 kvm_hv_flush_tlb(struct kvm_vcpu *vcpu, struct kvm_hv_hcall *hc)
{
struct kvm *kvm = vcpu->kvm;
@@ -1791,6 +1826,8 @@ 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;

/*
@@ -1870,10 +1907,20 @@ 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_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_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 1030b1b50552..f79edf9234cd 100644
--- a/arch/x86/kvm/hyperv.h
+++ b/arch/x86/kvm/hyperv.h
@@ -151,4 +151,19 @@ 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_purge_flush_tlb(struct kvm_vcpu *vcpu)
+{
+ struct kvm_vcpu_hv_tlb_flush_fifo *tlb_flush_fifo;
+ struct kvm_vcpu_hv *hv_vcpu = to_hv_vcpu(vcpu);
+
+ if (!hv_vcpu || !kvm_check_request(KVM_REQ_HV_TLB_FLUSH, vcpu))
+ return;
+
+ tlb_flush_fifo = &hv_vcpu->tlb_flush_fifo;
+
+ kfifo_reset_out(&tlb_flush_fifo->entries);
+}
+
+int kvm_hv_vcpu_flush_tlb(struct kvm_vcpu *vcpu);
+
#endif
diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index 64c5d2bc863f..c8d661c16d4f 100644
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -3742,7 +3742,7 @@ static void svm_flush_tlb_current(struct kvm_vcpu *vcpu)
* A TLB flush for the current ASID flushes both "host" and "guest" TLB
* entries, and thus is a superset of Hyper-V's fine grained flushing.
*/
- kvm_clear_request(KVM_REQ_HV_TLB_FLUSH, vcpu);
+ kvm_hv_vcpu_purge_flush_tlb(vcpu);

/*
* Flush only the current ASID even if the TLB flush was invoked via
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 0539d216f760..7fb8bd42b13e 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -3388,7 +3388,7 @@ static void kvm_vcpu_flush_tlb_all(struct kvm_vcpu *vcpu)
kvm_clear_request(KVM_REQ_TLB_FLUSH_CURRENT, 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;

@@ -3409,7 +3409,7 @@ static void kvm_vcpu_flush_tlb_guest(struct kvm_vcpu *vcpu)
* Flushing all "guest" TLB is always a superset of Hyper-V's fine
* grained flushing.
*/
- kvm_clear_request(KVM_REQ_HV_TLB_FLUSH, vcpu);
+ kvm_hv_vcpu_purge_flush_tlb(vcpu);
}

@@ -10484,7 +10484,14 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu)

kvm_service_local_tlb_flush_requests(vcpu);

- if (kvm_check_request(KVM_REQ_HV_TLB_FLUSH, vcpu))
+ /*
+ * Fall back to a "full" guest flush if Hyper-V's precise
+ * flushing fails. Note, Hyper-V's flushing is per-vCPU, but
+ * the flushes are considered "remote" and not "local" because
+ * the requests can be initiated from other vCPUs.
+ */
+ if (kvm_check_request(KVM_REQ_HV_TLB_FLUSH, vcpu) &&
+ kvm_hv_vcpu_flush_tlb(vcpu))
kvm_vcpu_flush_tlb_guest(vcpu);

if (kvm_check_request(KVM_REQ_REPORT_TPR_ACCESS, vcpu)) {
diff --git a/arch/x86/kvm/x86.h b/arch/x86/kvm/x86.h
index a784ff90740b..1ea28a7bdf2f 100644
--- a/arch/x86/kvm/x86.h
+++ b/arch/x86/kvm/x86.h
@@ -79,6 +79,7 @@ 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);

--
2.37.3