linux-kernel - Re: [PATCH 4/4] KVM: Improve warning report in mark_page_dirty_in

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite for Android: free password hash cracker in your pocket

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <d8e63ad9-e0e3-dbb1-b646-a1b5771d4c4b@redhat.com>
Date:   Thu, 19 Jan 2023 12:15:16 +1100
From:   Gavin Shan <gshan@...hat.com>
To:     Sean Christopherson <seanjc@...gle.com>
Cc:     kvmarm@...ts.linux.dev, kvmarm@...ts.cs.columbia.edu,
        kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        pbonzini@...hat.com, maz@...nel.org, corbet@....net,
        james.morse@....com, suzuki.poulose@....com,
        oliver.upton@...ux.dev, yuzenghui@...wei.com,
        catalin.marinas@....com, will@...nel.org, ricarkol@...gle.com,
        eric.auger@...hat.com, yuzhe@...china.com, renzhengeek@...il.com,
        ardb@...nel.org, peterx@...hat.com, shan.gavin@...il.com
Subject: Re: [PATCH 4/4] KVM: Improve warning report in
 mark_page_dirty_in_slot()

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