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From: Yazen Ghannam <yazen.ghannam@amd.com>
To: <mingo@kernel.org>, <tglx@linutronix.de>, <bp@suse.de>,
	<hpa@zytor.com>, <linux-kernel@vger.kernel.org>
Cc: <linux-tip-commits@vger.kernel.org>
Subject: Re: [tip:ras/core] x86/RAS: Simplify SMCA HWID descriptor struct
Date: Thu, 10 Nov 2016 12:50:04 -0500	[thread overview]
Message-ID: <20161110175004.lji5k53ccli7gjig@yaz-fedora.dyhomenet> (raw)
In-Reply-To: <tip-1ce9cd7f9f0b71af7c496b816734bc2dc699363a@git.kernel.org>

>  static void get_smca_bank_info(unsigned int bank)
>  {
>  	unsigned int i, hwid_mcatype, cpu = smp_processor_id();
> -	struct smca_hwid_mcatype *type;
> +	struct smca_hwid *s_hwid;
>  	u32 high, instance_id;
> -	u16 hwid, mcatype;
>  
>  	/* Collect bank_info using CPU 0 for now. */
>  	if (cpu)
> @@ -162,14 +157,13 @@ static void get_smca_bank_info(unsigned int bank)
>  		return;
>  	}
>  
> -	hwid = high & MCI_IPID_HWID;
> -	mcatype = (high & MCI_IPID_MCATYPE) >> 16;
> -	hwid_mcatype = HWID_MCATYPE(hwid, mcatype);
> +	hwid_mcatype = HWID_MCATYPE(high & MCI_IPID_HWID,
> +				    (high & MCI_IPID_MCATYPE) >> 16);
>

Sorry for catching this late, but it seems this change doesn't compile
correctly. This causes the value of hwid_mcatype to be incorrect, so we
will never match a bank to its type.

I see this with GCC 4.8.5 and 5.4.0. 

There are no warnings or issues when building or booting just
that the behavior is incorrect. 

Disassembly of above change:
      db:       8b 45 e0                mov    -0x20(%rbp),%eax
      de:       41 89 c4                mov    %eax,%r12d
      e1:       25 00 00 ff 0f          and    $0xfff0000,%eax
      e6:       41 c1 ec 10             shr    $0x10,%r12d
      ea:       41 09 c4                or     %eax,%r12d

Disassembly of original code:
     286:       8b 45 d0                mov    -0x30(%rbp),%eax
     289:       41 89 c5                mov    %eax,%r13d
     28c:       c1 e8 10                shr    $0x10,%eax
     28f:       41 81 e5 ff 0f 00 00    and    $0xfff,%r13d
     296:       41 c1 e5 10             shl    $0x10,%r13d
     29a:       41 09 c5                or     %eax,%r13d

Adding extra parentheses in HWID_MCATYPE() gives the same assembly as the
original code and fixes the behavior.

> +	hwid_mcatype = HWID_MCATYPE((high & MCI_IPID_HWID)),
> +				    ((high & MCI_IPID_MCATYPE) >> 16));

Thanks,
Yazen

  reply	other threads:[~2016-11-10 19:21 UTC|newest]

Thread overview: 13+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-11-03 12:55 [PATCH 1/3] x86/RAS: Simplify SMCA bank " Borislav Petkov
2016-11-03 12:55 ` [PATCH 2/3] x86/RAS: Simplify SMCA HWID " Borislav Petkov
2016-11-08 16:20   ` [tip:ras/core] " tip-bot for Borislav Petkov
2016-11-10 17:50     ` Yazen Ghannam [this message]
2016-11-10 17:57       ` Borislav Petkov
2016-11-10 19:53         ` Thomas Gleixner
2016-11-10 20:12           ` Yazen Ghannam
2016-11-03 12:55 ` [PATCH 3/3] x86/RAS: Rename smca_bank_names to smca_names Borislav Petkov
2016-11-08 16:21   ` [tip:ras/core] " tip-bot for Borislav Petkov
2016-11-04 14:44 ` [PATCH 1/3] x86/RAS: Simplify SMCA bank descriptor struct Yazen Ghannam
2016-11-04 15:23   ` Borislav Petkov
2016-11-08 16:21     ` [tip:ras/core] x86/RAS: Hide SMCA bank names tip-bot for Borislav Petkov
2016-11-08 16:20 ` [tip:ras/core] x86/RAS: Simplify SMCA bank descriptor struct tip-bot for Borislav Petkov

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