Re: [RFC][PATCH] arm64: tlb: call kvm_call_hyp once during kvm_tlb_flush_vmid_range

On Mon, 09 Feb 2026 13:14:07 +0000,
"yezhenyu (A)" [off-list ref] wrote:

From 9982be89f55bd99b3683337223284f0011ed248e Mon Sep 17 00:00:00 2001
From: eillon <redacted>
Date: Mon, 9 Feb 2026 19:48:46 +0800
Subject: [RFC][PATCH v1] arm64: tlb: call kvm_call_hyp once during
 kvm_tlb_flush_vmid_range

The kvm_tlb_flush_vmid_range() function is performance-critical
during live migration, but there is a while loop when the system
support flush tlb by range when the size is larger than MAX_TLBI_RANGE_PAGES.

This results in frequent entry to kvm_call_hyp() and then a large

What is the cost of kvm_call_hyp()?

amount of time is spent in kvm_clear_dirty_log_protect() during
migration(more than 50%).

50% of what time? The guest's run-time? The time spent doing TLBIs
compared to the time spent in kvm_clear_dirty_log_protect()?

So, when the address range is large than
MAX_TLBI_RANGE_PAGES, directly call __kvm_tlb_flush_vmid to
optimize performance.

Multiple things here:

- there is no SoB, which means that patch cannot be considered for
  merging

- there is no data showing how this change improves the situation for
  a large enough set of workloads

- there is no description of a test that could be run on multiple
  implementations to check whether this change has a positive or
  negative impact

If you want to progress this sort of things, you will need to address
these points.

Thanks,

	M.

-- 
Without deviation from the norm, progress is not possible.