linux-kernel - Re: [PATCH Part2 v6 02/49] iommu/amd: Introduce function to check SEV-SNP support

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Date:   Sun, 28 Aug 2022 07:18:02 +0300
From:   Jarkko Sakkinen <jarkko@...nel.org>
To:     "Kalra, Ashish" <Ashish.Kalra@....com>
Cc:     Peter Gonda <pgonda@...gle.com>,
        the arch/x86 maintainers <x86@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        kvm list <kvm@...r.kernel.org>,
        "linux-coco@...ts.linux.dev" <linux-coco@...ts.linux.dev>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        Linux Crypto Mailing List <linux-crypto@...r.kernel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Joerg Roedel <jroedel@...e.de>,
        "Lendacky, Thomas" <Thomas.Lendacky@....com>,
        "H. Peter Anvin" <hpa@...or.com>, Ard Biesheuvel <ardb@...nel.org>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Andy Lutomirski <luto@...nel.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Sergio Lopez <slp@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>,
        David Rientjes <rientjes@...gle.com>,
        Dov Murik <dovmurik@...ux.ibm.com>,
        Tobin Feldman-Fitzthum <tobin@....com>,
        Borislav Petkov <bp@...en8.de>,
        "Roth, Michael" <Michael.Roth@....com>,
        Vlastimil Babka <vbabka@...e.cz>,
        "Kirill A . Shutemov" <kirill@...temov.name>,
        Andi Kleen <ak@...ux.intel.com>,
        Tony Luck <tony.luck@...el.com>, Marc Orr <marcorr@...gle.com>,
        Sathyanarayanan Kuppuswamy 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>,
        Alper Gun <alpergun@...gle.com>,
        "Dr. David Alan Gilbert" <dgilbert@...hat.com>
Subject: Re: [PATCH Part2 v6 02/49] iommu/amd: Introduce function to check
 SEV-SNP support

On Fri, Aug 26, 2022 at 06:54:16PM +0000, Kalra, Ashish wrote:
> [AMD Official Use Only - General]
> 
> Hello Jarkko,
> 
> >> 
> >> It really should be, in order to have any practical use:
> >> 
> >> 	if (no_iommu) {
> >> 		pr_err("SEV-SNP: IOMMU is disabled.\n");
> >> 		return false;
> >> 	}
> >> 
> >> 	if (iommu_default_passthrough()) {
> >> 		pr_err("SEV-SNP: IOMMU is configured in passthrough mode.\n");
> >> 		return false;
> >> 	}
> >> 
> >> The comment is *completely* redundant, it absolutely does not serve 
> >> any sane purpose. It just tells what the code already clearly stating.
> >> 
> >> The combo error message on the other hand leaves you to the question 
> >> "which one was it", and for that reason combining the checks leaves 
> >> you to a louse debugging experience.
> 
> >Also, are those really *errors*? That implies that there is something wrong.
> 
> >Since you can have a legit configuration, IMHO they should be either warn or info. What do you think?
> 
> >They are definitely not errors
> 
> Yes, they can be warn or info, but as I mentioned above this patch is now part of IOMMU + SNP series,
> so these comments are now relevant for that.

Yeah, warn/info/error is less relevant than the
second point I was making.

It's a good idea to spit out two instead of one
to make best of spitting out anything in the first
place :-) That way you make no mistake interpreting
what does the log message connect to, which can
sometimes make a difference while debugging a
kernel issue.

BR, Jarkko