|
Message-ID: <20170220072130.GB8974@gmail.com> Date: Mon, 20 Feb 2017 08:21:30 +0100 From: Ingo Molnar <mingo@...nel.org> To: Kees Cook <keescook@...omium.org> Cc: Pavel Machek <pavel@....cz>, Laura Abbott <labbott@...hat.com>, Mark Rutland <mark.rutland@....com>, "linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>, Catalin Marinas <catalin.marinas@....com>, Heiko Carstens <heiko.carstens@...ibm.com>, "James E.J. Bottomley" <jejb@...isc-linux.org>, "H. Peter Anvin" <hpa@...or.com>, "kernel-hardening@...ts.openwall.com" <kernel-hardening@...ts.openwall.com>, Rob Herring <robh@...nel.org>, Jessica Yu <jeyu@...hat.com>, Jonathan Corbet <corbet@....net>, Helge Deller <deller@....de>, "x86@...nel.org" <x86@...nel.org>, Russell King <linux@...linux.org.uk>, Ingo Molnar <mingo@...hat.com>, Len Brown <len.brown@...el.com>, "linux-s390@...r.kernel.org" <linux-s390@...r.kernel.org>, Will Deacon <will.deacon@....com>, Thomas Gleixner <tglx@...utronix.de>, "linux-arm-kernel@...ts.infradead.org" <linux-arm-kernel@...ts.infradead.org>, linux-parisc <linux-parisc@...r.kernel.org>, Linux PM list <linux-pm@...r.kernel.org>, "Rafael J. Wysocki" <rjw@...ysocki.net>, LKML <linux-kernel@...r.kernel.org>, Jason Wessel <jason.wessel@...driver.com>, Martin Schwidefsky <schwidefsky@...ibm.com>, Robin Murphy <robin.murphy@....com> Subject: Re: [PATCHv3 2/2] arch: Rename CONFIG_DEBUG_RODATA and CONFIG_DEBUG_MODULE_RONX * Kees Cook <keescook@...omium.org> wrote: > On Thu, Feb 16, 2017 at 2:25 PM, Pavel Machek <pavel@....cz> wrote: > > Hi! > > > >> > >> -config DEBUG_RODATA > >> +config STRICT_KERNEL_RWX > >> bool "Make kernel text and rodata read-only" if ARCH_OPTIONAL_KERNEL_RWX > >> depends on ARCH_HAS_STRICT_KERNEL_RWX > >> default !ARCH_OPTIONAL_KERNEL_RWX || > > > > Debug features are expected to have runtime cost, so kconfig help is > > silent about those. But there are runtime costs, right? It would be > > nice to mention them in the help text... > > It depends on the architecture. The prior help text for arm said: > > The tradeoff is that each region is padded to section-size (1MiB) > boundaries (because their permissions are different and splitting > the 1M pages into 4K ones causes TLB performance problems), which > can waste memory. > > parisc (somewhat inaccurately) said: > > This option may have a slight performance impact because a > portion of the kernel code won't be covered by a TLB anymore. > > IIUC, arm64 does what parisc is hinting at: mappings at the end are > broken down to PAGE_SIZE. On x86, IIUC, there's actually no change to > TLB performance due to how the mappings are already set up. BTW., a good strategy with RAM sizes above say 4GB would be to just round up to the next large-TLB boundary (2MB) and waste 0-2MB of RAM - which is only 0.05% of 4GB of RAM. On most workloads, especially with SSDs it's probably a positive RAM vs. performance trade-off. Thanks, Ingo
Powered by blists - more mailing lists
Confused about mailing lists and their use? Read about mailing lists on Wikipedia and check out these guidelines on proper formatting of your messages.