Re: [RFC PATCH v2 6/8] KVM: arm64: Only write protect selected PTE

[Catalin Marinas <catalin.marinas@arm.com>]

On Fri, Aug 25, 2023 at 10:35:26AM +0100, Shameer Kolothum wrote:
> From: Keqian Zhu <zhukeqian1@huawei.com>
> 
> This function write protects all PTEs between the ffs and fls of mask.
> There may be unset bits between this range. It works well under pure
> software dirty log, as software dirty log is not working during this
> process.
> 
> But it will unexpectly clear dirty status of PTE when hardware dirty
> log is enabled. So change it to only write protect selected PTE.

Ah, I did wonder about losing the dirty status. The equivalent to S1
would be for kvm_pgtable_stage2_wrprotect() to set a software dirty bit.

I'm only superficially familiar with how KVM does dirty tracking for
live migration. Does it need to first write-protect the pages and
disable DBM? Is DBM re-enabled later? Or does stage2_wp_range() with
your patches leave the DBM on? If the latter, the 'wp' aspect is a bit
confusing since DBM basically means writeable (and maybe clean). So
better to have something like stage2_clean_range().

-- 
Catalin