From mboxrd@z Thu Jan 1 00:00:00 1970 From: james.morse@arm.com (James Morse) Date: Fri, 8 Jun 2018 18:44:10 +0100 Subject: [PATCH v4 3/3] arm64: Introduce command line parameter to disable CNP In-Reply-To: References: <1526638022-4137-1-git-send-email-vladimir.murzin@arm.com> <1526638022-4137-4-git-send-email-vladimir.murzin@arm.com> <20180523171721.ppazcyf576koimhl@armageddon.cambridge.arm.com> Message-ID: To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org Hi Vladimir, Catalin, On 24/05/18 09:20, Vladimir Murzin wrote: > On 23/05/18 18:17, Catalin Marinas wrote: >> On Fri, May 18, 2018 at 11:07:02AM +0100, Vladimir Murzin wrote: >>> diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt >>> index 11fc28e..8f59d47 100644 >>> --- a/Documentation/admin-guide/kernel-parameters.txt >>> +++ b/Documentation/admin-guide/kernel-parameters.txt >>> @@ -2636,6 +2636,10 @@ >>> + nocnp [ARM64] >>> + Disable CNP (Common not Private translations) >>> + even if it is supported by processor. >> Do we actually have a use-case for this command line option? I'm not >> considering hardware errata as these are handled separately in the >> kernel. > Well, I cannot count all cases, yet we might see CnP support advertised > by CPU via ID register (where CPU meant to be part of bL) but not really > doing optimisations in hardware. > > Probably, some userspace (benchmarks) might not benefit of CnP; otoh maybe > better way for such case would be user-space asking kernel to {dis,en}able > CnP... > > I have no strong opinion on patch, so I'm fine to drop it and come back > when/if we get results from real hardware. We may want to disable CNP without rebuilding the kernel, which would also have the affect of code-layout changes... Thanks, James