linux-kernel - Re: [PATCH Part2 RFC v4 09/40] x86/fault: Add support to dump RMP entry on fault

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Date:   Thu, 8 Jul 2021 12:11:13 -0500
From:   Brijesh Singh <brijesh.singh@....com>
To:     Dave Hansen <dave.hansen@...el.com>, x86@...nel.org,
        linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        linux-efi@...r.kernel.org, platform-driver-x86@...r.kernel.org,
        linux-coco@...ts.linux.dev, linux-mm@...ck.org,
        linux-crypto@...r.kernel.org
Cc:     brijesh.singh@....com, Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Joerg Roedel <jroedel@...e.de>,
        Tom Lendacky <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 Gonda <pgonda@...gle.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>,
        Michael Roth <michael.roth@....com>,
        Vlastimil Babka <vbabka@...e.cz>, tony.luck@...el.com,
        npmccallum@...hat.com, brijesh.ksingh@...il.com
Subject: Re: [PATCH Part2 RFC v4 09/40] x86/fault: Add support to dump RMP
 entry on fault



On 7/8/21 11:58 AM, Dave Hansen wrote:>> Logically its going to be 
tricky to figure out which exact entry caused
>> the fault, hence I dump any non-zero entry. I understand it may dump
>> some useless.
> 
> What's tricky about it?
> 
> Sure, there's a possibility that more than one entry could contribute to
> a fault.  But, you always know *IF* an entry could contribute to a fault.
> 
> I'm fine if you run through the logic, don't find a known reason
> (specific RMP entry) for the fault, and dump the whole table in that
> case.  But, unconditionally polluting the kernel log with noise isn't
> very nice for debugging.

The tricky part is to determine which undocumented bit to check to know 
that we should stop dump. I can go with your suggestion that first try 
with the known reasons and fallback to dump whole table for unknown 
reasons only.

thanks