KVM: x86: hyper-v: Introduce TLB flush fifo

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.

Reviewed-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Message-Id: <20221101145426.251680-10-vkuznets@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

1 files changed, 20 insertions, 0 deletions

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index 0b85230a0e0a..3e35dcf40dc7 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>
@@ -618,6 +619,23 @@ 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;
@@ -639,6 +657,8 @@ 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 */