Maxim Levitsky [off-list ref] writes:

On Thu, 2022-04-14 at 15:19 +0200, Vitaly Kuznetsov wrote:

quoted

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.

As I see from this patch, also the code doesn't process the requests
from the ring buffer yet, but rather just ignores it completely,
and resets the whole ring buffer (kvm_hv_vcpu_empty_flush_tlb)
Maybe you should mention it here.

quoted

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;
+};

Have you considered using kfifo.h library instead?

As a matter of fact I have not and this is a good suggestion,
actually. Let me try to use it instead of my home-brewed ring. I'll
address your other comments after that. Thanks!

-- 
Vitaly