linux-kernel - Re: [PATCH] KVM: SVM: Only dump VSMA to klog for debugging

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Message-ID: <Y2Q/3A1DSzSJkRAy@google.com>
Date:   Thu, 3 Nov 2022 22:25:32 +0000
From:   Sean Christopherson <seanjc@...gle.com>
To:     Peter Gonda <pgonda@...gle.com>
Cc:     jarkko@...nel.org, Harald Hoyer <harald@...fian.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
        "H. Peter Anvin" <hpa@...or.com>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] KVM: SVM: Only dump VSMA to klog for debugging

On Thu, Nov 03, 2022, Peter Gonda wrote:
> The KERN_CONT documentation says it defaults back to KERNL_DEFAULT if the

State what actually happens.  Documentation is sometimes wrong, and just saying
"the docs say XYZ" makes it sound like this is a fix based on code inspection,
whereas you encountered a real problem.  E.g.

  Explicitly print the VMSA dump at KERN_DEBUG log level, KERN_CONT uses
  KERNEL_DEFAULT if the previous log line has a newline, i.e. if there's
  nothing to continuing, and as a result the VMSA gets dumped when it
  shouldn't.

> previous log line has a newline. So switch from KERN_CONT to
> print_hex_dump_debug().

Jarkko pointed this out in the original submission, but the buggy patch got queued
without the fixup.  This is a good opportunity to throw in a link so that it's
clear that the change is aligned with the original intent.

  Link: https://lore.kernel.org/all/YuPMeWX4uuR1Tz3M@kernel.org

> Cc: Jarkko Sakkinen <jarkko@...nel.org>
> Cc: Harald Hoyer <harald@...fian.com>
> Cc: Paolo Bonzini <pbonzini@...hat.com>
> Cc: Sean Christopherson <seanjc@...gle.com>
> Cc: Thomas Gleixner <tglx@...utronix.de>
> Cc: Ingo Molnar <mingo@...hat.com>
> Cc: Borislav Petkov <bp@...en8.de>
> Cc: Dave Hansen <dave.hansen@...ux.intel.com>
> Cc: x86@...nel.org
> Cc: "H. Peter Anvin" <hpa@...or.com>
> Cc: kvm@...r.kernel.org
> Cc: linux-kernel@...r.kernel.org
> Signed-off-by: Peter Gonda <pgonda@...gle.com>
> 
> Fixes: 6fac42f127b8 ("KVM: SVM: Dump Virtual Machine Save Area (VMSA) to klog")

Fixes: usually goes before everything else, and this should probably Cc stable@
as well.

With the above tweaks,

Reviewed-by: Sean Christopherson <seanjc@...gle.com>