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Reply-To: Gavin Shan <gshan@redhat.com>
Subject: Re: [PATCH 4/4] KVM: Improve warning report in
 mark_page_dirty_in_slot()
To:     Sean Christopherson <seanjc@google.com>
Cc:     kvmarm@lists.linux.dev, kvmarm@lists.cs.columbia.edu,
        kvm@vger.kernel.org, linux-kernel@vger.kernel.org,
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References: <20230116040405.260935-1-gshan@redhat.com>
 <20230116040405.260935-5-gshan@redhat.com> <Y8bBzKF17IdZP9eF@google.com>
From:   Gavin Shan <gshan@redhat.com>
Message-ID: <d8e63ad9-e0e3-dbb1-b646-a1b5771d4c4b@redhat.com>
Date:   Thu, 19 Jan 2023 12:15:16 +1100
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Hi Sean,

On 1/18/23 2:42 AM, Sean Christopherson wrote:
> On Mon, Jan 16, 2023, Gavin Shan wrote:
>> There are two warning reports about the dirty ring in the function.
>> We have the wrong assumption that the dirty ring is always enabled when
>> CONFIG_HAVE_KVM_DIRTY_RING is selected.
> 
> No, it's not a wrong assumption, becuase it's not an assumption.  The intent is
> to warn irrespective of dirty ring/log enabling.  The orignal code actually warned
> irrespective of dirty ring support[1], again intentionally.  The
> CONFIG_HAVE_KVM_DIRTY_RING check was added because s390 can mark pages dirty from
> an worker thread[2] and s390 has no plans to support the dirty ring.
> 
> The reason for warning even if dirty ring isn't enabled is so that bots can catch
> potential KVM bugs without having to set up a dirty ring or enable dirty logging.
> 
> [1] 2efd61a608b0 ("KVM: Warn if mark_page_dirty() is called without an active vCPU")
> [2] e09fccb5435d ("KVM: avoid warning on s390 in mark_page_dirty")
> 

Thanks for the linker. I was confused when looking at the code, but now it's clear to
me. Thanks for your explanation. How about to add a comment there?

   /*
    * The warning is expected when the dirty ring is configured,
    * but not enabled.
    */

Thanks,
Gavin