linux-kernel - Re: [PATCH v2 16/22] arm64/debug: Make use of the system wide safe value

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Message-ID: <20151008150819.GL17192@e104818-lin.cambridge.arm.com>
Date:	Thu, 8 Oct 2015 16:08:19 +0100
From:	Catalin Marinas <catalin.marinas@....com>
To:	"Suzuki K. Poulose" <Suzuki.Poulose@....com>
Cc:	mark.rutland@....com, Vladimir.Murzin@....com,
	steve.capper@...aro.org, ard.biesheuvel@...aro.org,
	marc.zyngier@....com, andre.przywara@....com, will.deacon@....com,
	linux-kernel@...r.kernel.org, edward.nevill@...aro.org,
	aph@...hat.com, james.morse@....com, dave.martin@....com,
	linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v2 16/22] arm64/debug: Make use of the system wide safe
 value

On Thu, Oct 08, 2015 at 12:56:28PM +0100, Suzuki K. Poulose wrote:
> On 08/10/15 12:11, Catalin Marinas wrote:
> >On Mon, Oct 05, 2015 at 06:02:05PM +0100, Suzuki K. Poulose wrote:
> >>@@ -137,13 +138,17 @@ extern struct pmu perf_ops_bp;
> >>  /* Determine number of BRP registers available. */
> >>  static inline int get_num_brps(void)
> >>  {
> >>-	return ((read_cpuid(ID_AA64DFR0_EL1) >> 12) & 0xf) + 1;
> >>+	return 1 +
> >>+		cpuid_feature_extract_field(read_system_reg(SYS_ID_AA64DFR0_EL1),
> >>+						ID_AA64DFR0_BRPS_SHIFT);
> >>  }
> >
> >cpuid_feature_extract_field() is fine but we should we bother with
> >read_system_reg vs just read_cpuid?
> >Similar question for patch 17/22.
> 
> Well, we would have already TAINTed the kernel, if these fields are different.
> It is just the matter of, whether we want to provide the safer value on a tainted
> kernel or not. I am open to suggestions.

Ah, sorry, I mixed read_system_reg() with read_cpu_sysreg(). I think we
need to rename the latter as it gets confusing. Maybe something like
read_native_sys_reg() or __raw_read_system_reg().

-- 
Catalin
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