Extended GVA ranges support bit seems to indicate whether lower 12
bits of GVA can be used to specify up to 4095 additional consequent
GVAs to flush. This is somewhat described in TLFS.

Previously, KVM was handling HVCALL_FLUSH_VIRTUAL_ADDRESS_LIST{,EX}
requests by flushing the whole VPID so technically, extended GVA
ranges were already supported. As such requests are handled more
gently now, advertizing support for extended ranges starts making
sense to reduce the size of TLB flush requests.

Reviewed-by: Maxim Levitsky <redacted>
Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
---
 arch/x86/include/asm/hyperv-tlfs.h | 2 ++
 arch/x86/kvm/hyperv.c              | 1 +
 2 files changed, 3 insertions(+)

diff --git a/arch/x86/include/asm/hyperv-tlfs.h b/arch/x86/include/asm/hyperv-tlfs.h
index 3089ec352743..d0fd106e51e6 100644
--- a/arch/x86/include/asm/hyperv-tlfs.h
+++ b/arch/x86/include/asm/hyperv-tlfs.h

@@ -61,6 +61,8 @@
 #define HV_FEATURE_GUEST_CRASH_MSR_AVAILABLE		BIT(10)
 /* Support for debug MSRs available */
 #define HV_FEATURE_DEBUG_MSRS_AVAILABLE			BIT(11)
+/* Support for extended gva ranges for flush hypercalls available */
+#define HV_FEATURE_EXT_GVA_RANGES_FLUSH			BIT(14)
 /*
  * Support for returning hypercall output block via XMM
  * registers is available

diff --git a/arch/x86/kvm/hyperv.c b/arch/x86/kvm/hyperv.c
index d5a329cebcc6..aced2b3fe56b 100644
--- a/arch/x86/kvm/hyperv.c
+++ b/arch/x86/kvm/hyperv.c

@@ -2636,6 +2636,7 @@ int kvm_get_hv_cpuid(struct kvm_vcpu *vcpu, struct kvm_cpuid2 *cpuid,
 			ent->ebx |= HV_DEBUGGING;
 			ent->edx |= HV_X64_GUEST_DEBUGGING_AVAILABLE;
 			ent->edx |= HV_FEATURE_DEBUG_MSRS_AVAILABLE;
+			ent->edx |= HV_FEATURE_EXT_GVA_RANGES_FLUSH;
 
 			/*
 			 * Direct Synthetic timers only make sense with in-kernel

-- 
2.37.3