linux-kernel - Re: [PATCH v1 3/5] KVM: selftests: Dirty host pages in dirty_log

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Date:   Fri, 19 Aug 2022 07:28:05 +0200
From:   Andrew Jones <andrew.jones@...ux.dev>
To:     Gavin Shan <gshan@...hat.com>
Cc:     kvmarm@...ts.cs.columbia.edu, linux-arm-kernel@...ts.infradead.org,
        kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-doc@...r.kernel.org, linux-kselftest@...r.kernel.org,
        peterx@...hat.com, pbonzini@...hat.com, corbet@....net,
        maz@...nel.org, james.morse@....com, alexandru.elisei@....com,
        suzuki.poulose@....com, oliver.upton@...ux.dev,
        catalin.marinas@....com, will@...nel.org, shuah@...nel.org,
        seanjc@...gle.com, drjones@...hat.com, dmatlack@...gle.com,
        bgardon@...gle.com, ricarkol@...gle.com, zhenyzha@...hat.com,
        shan.gavin@...il.com
Subject: Re: [PATCH v1 3/5] KVM: selftests: Dirty host pages in dirty_log_test

On Fri, Aug 19, 2022 at 08:55:59AM +0800, Gavin Shan wrote:
> It's assumed that 1024 host pages, instead of guest pages, are dirtied
> in each iteration in guest_code(). The current implementation misses
> the case of mismatched page sizes in host and guest. For example,
> ARM64 could have 64KB page size in guest, but 4KB page size in host.
> (TEST_PAGES_PER_LOOP / 16), instead of TEST_PAGES_PER_LOOP, host pages
> are dirtied in every iteration.
> 
> Fix the issue by touching all sub-pages when we have mismatched
> page sizes in host and guest.

I'll let the dirty-log test authors decide what's best to do for this
test, but I'd think we should let the guest continue dirtying its
pages without knowledge of the host pages. Then, adjust the host test
code to assert all sub-pages, other than the ones it expects the guest
to have written, remain untouched.

Thanks,
drew