Messages in this thread | | | From | "Ghannam, Yazen" <> | Subject | RE: [PATCH] x86/MCE, EDAC/mce_amd: Save all aux registers on SMCA systems | Date | Fri, 20 Apr 2018 13:05:17 +0000 |
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> -----Original Message----- > From: Borislav Petkov <bp@alien8.de> > Sent: Wednesday, April 18, 2018 1:14 PM > To: Ghannam, Yazen <Yazen.Ghannam@amd.com> > Cc: linux-edac@vger.kernel.org; linux-kernel@vger.kernel.org; > tony.luck@intel.com; x86@kernel.org > Subject: Re: [PATCH] x86/MCE, EDAC/mce_amd: Save all aux registers on > SMCA systems > > On Tue, Apr 17, 2018 at 06:30:34PM +0000, Ghannam, Yazen wrote: > > We could but it's an issue of documentation and testing the older systems. > > > > My first pass at this was to unconditionally read the registers because my > > understanding was that registers that aren't accessible would be read-as- > zero. > > I thought this was a common MCA implementation. But Tony pointed out > that > > this isn't the case on Intel systems. This is the case on recent AMD systems. > But > > I don't know if it's the case on older systems which may or may not have > > followed the Intel implementation more closely. > > So if our worry is the #GPs, we can always use the rdmsr*_safe() > variants and look at the return value. And dump a invalid value like > 0xdeadbeef or so, if the read failed. > > But if any bit of info we've gotten this way, helps us debug an MCE, > we're already golden! >
Okay, I can do that. What about using mce_rdmsrl()? The value gets set to 0 and a user gets a single warning. This may be more clear to the user. Also, it shouldn't affect code that checks for non-zero values, like in __print_mce().
> > For example, > > > > Deferred error occurs: > > - MCA_{STATUS,ADDR,DESTAT,DEADDR} all have valid data. > > > > MCE occurs > > - MCA_{STATUS,ADDR} are overwritten with non-zero data. > > - MCE handler clears MCA_STATUS. MCA_ADDR is non-zero. > > > > DFR handler finds MCA_STATUS[Deferred] is clear, so it saves > > MCA_DESTAT and MCA_DEADDR which is 0. > > > > If !m->addr (which has MCA_DEADDR), then we read MCA_STATUS > > which has the address from the MCE. > > The code could use a shorter version of this as a comment to state why > we're doing it. Because it is not obvious. >
Yes, will do.
Thanks, Yazen
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