* [PATCH] arm64: Allow user selection of ARM64_MODULE_PLTS @ 2019-06-14 2:59 Florian Fainelli 2019-06-14 7:02 ` Ard Biesheuvel 2019-06-17 17:32 ` Will Deacon 0 siblings, 2 replies; 5+ messages in thread From: Florian Fainelli @ 2019-06-14 2:59 UTC (permalink / raw) To: linux-arm-kernel Cc: Florian Fainelli, ard.biesheuvel, Catalin Marinas, Will Deacon, open list, bcm-kernel-feedback-list, moderated list:ARM64 PORT AARCH64 ARCHITECTURE Make ARM64_MODULE_PLTS a selectable Kconfig symbol, since some people might have very big modules spilling out of the dedicated module area into vmalloc. Help text is copied from the ARM 32-bit counterpart. Signed-off-by: Florian Fainelli <f.fainelli@gmail.com> --- arch/arm64/Kconfig | 14 +++++++++++++- 1 file changed, 13 insertions(+), 1 deletion(-) diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig index 697ea0510729..36befe987b73 100644 --- a/arch/arm64/Kconfig +++ b/arch/arm64/Kconfig @@ -1418,8 +1418,20 @@ config ARM64_SVE KVM in the same kernel image. config ARM64_MODULE_PLTS - bool + bool "Use PLTs to allow module memory to spill over into vmalloc area" select HAVE_MOD_ARCH_SPECIFIC + help + Allocate PLTs when loading modules so that jumps and calls whose + targets are too far away for their relative offsets to be encoded + in the instructions themselves can be bounced via veneers in the + module's PLT. This allows modules to be allocated in the generic + vmalloc area after the dedicated module memory area has been + exhausted. The modules will use slightly more memory, but after + rounding up to page size, the actual memory footprint is usually + the same. + + Disabling this is usually safe for small single-platform + configurations. If unsure, say y. config ARM64_PSEUDO_NMI bool "Support for NMI-like interrupts" -- 2.17.1 _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel ^ permalink raw reply related [flat|nested] 5+ messages in thread
* Re: [PATCH] arm64: Allow user selection of ARM64_MODULE_PLTS 2019-06-14 2:59 [PATCH] arm64: Allow user selection of ARM64_MODULE_PLTS Florian Fainelli @ 2019-06-14 7:02 ` Ard Biesheuvel 2019-06-17 17:32 ` Will Deacon 1 sibling, 0 replies; 5+ messages in thread From: Ard Biesheuvel @ 2019-06-14 7:02 UTC (permalink / raw) To: Florian Fainelli Cc: Catalin Marinas, Will Deacon, open list, bcm-kernel-feedback-list, linux-arm-kernel, moderated list:ARM64 PORT (AARCH64 ARCHITECTURE) On Fri, 14 Jun 2019 at 04:59, Florian Fainelli <f.fainelli@gmail.com> wrote: > > Make ARM64_MODULE_PLTS a selectable Kconfig symbol, since some people > might have very big modules spilling out of the dedicated module area > into vmalloc. Help text is copied from the ARM 32-bit counterpart. > > Signed-off-by: Florian Fainelli <f.fainelli@gmail.com> > --- > arch/arm64/Kconfig | 14 +++++++++++++- > 1 file changed, 13 insertions(+), 1 deletion(-) > > diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig > index 697ea0510729..36befe987b73 100644 > --- a/arch/arm64/Kconfig > +++ b/arch/arm64/Kconfig > @@ -1418,8 +1418,20 @@ config ARM64_SVE > KVM in the same kernel image. > > config ARM64_MODULE_PLTS > - bool > + bool "Use PLTs to allow module memory to spill over into vmalloc area" > select HAVE_MOD_ARCH_SPECIFIC > + help > + Allocate PLTs when loading modules so that jumps and calls whose > + targets are too far away for their relative offsets to be encoded > + in the instructions themselves can be bounced via veneers in the > + module's PLT. This allows modules to be allocated in the generic > + vmalloc area after the dedicated module memory area has been > + exhausted. The modules will use slightly more memory, but after > + rounding up to page size, the actual memory footprint is usually > + the same. > + > + Disabling this is usually safe for small single-platform > + configurations. If unsure, say y. > I don't mind adding this, but it makes sense to add an explanation why KASLR enables this. E.g., """ When running with address space randomization (KASLR), the module region itself may be too far away for ordinary relative jumps and calls, and so in that case, module PLTs are required and cannot be disabled. """ > config ARM64_PSEUDO_NMI > bool "Support for NMI-like interrupts" > -- > 2.17.1 > _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel ^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [PATCH] arm64: Allow user selection of ARM64_MODULE_PLTS 2019-06-14 2:59 [PATCH] arm64: Allow user selection of ARM64_MODULE_PLTS Florian Fainelli 2019-06-14 7:02 ` Ard Biesheuvel @ 2019-06-17 17:32 ` Will Deacon 2019-06-17 18:03 ` Florian Fainelli 1 sibling, 1 reply; 5+ messages in thread From: Will Deacon @ 2019-06-17 17:32 UTC (permalink / raw) To: Florian Fainelli Cc: ard.biesheuvel, Catalin Marinas, open list, bcm-kernel-feedback-list, linux-arm-kernel, moderated list:ARM64 PORT (AARCH64 ARCHITECTURE) On Thu, Jun 13, 2019 at 07:59:32PM -0700, Florian Fainelli wrote: > Make ARM64_MODULE_PLTS a selectable Kconfig symbol, since some people > might have very big modules spilling out of the dedicated module area > into vmalloc. Help text is copied from the ARM 32-bit counterpart. > > Signed-off-by: Florian Fainelli <f.fainelli@gmail.com> > --- > arch/arm64/Kconfig | 14 +++++++++++++- > 1 file changed, 13 insertions(+), 1 deletion(-) > > diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig > index 697ea0510729..36befe987b73 100644 > --- a/arch/arm64/Kconfig > +++ b/arch/arm64/Kconfig > @@ -1418,8 +1418,20 @@ config ARM64_SVE > KVM in the same kernel image. > > config ARM64_MODULE_PLTS > - bool > + bool "Use PLTs to allow module memory to spill over into vmalloc area" > select HAVE_MOD_ARCH_SPECIFIC > + help > + Allocate PLTs when loading modules so that jumps and calls whose > + targets are too far away for their relative offsets to be encoded > + in the instructions themselves can be bounced via veneers in the > + module's PLT. This allows modules to be allocated in the generic > + vmalloc area after the dedicated module memory area has been > + exhausted. The modules will use slightly more memory, but after > + rounding up to page size, the actual memory footprint is usually > + the same. Isn't the worry really about the runtime performance overhead introduced by the veneers, as opposed to the memory usage of the module? > + Disabling this is usually safe for small single-platform > + configurations. If unsure, say y. So should this be on by default? Will _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel ^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [PATCH] arm64: Allow user selection of ARM64_MODULE_PLTS 2019-06-17 17:32 ` Will Deacon @ 2019-06-17 18:03 ` Florian Fainelli 2019-06-17 18:10 ` Will Deacon 0 siblings, 1 reply; 5+ messages in thread From: Florian Fainelli @ 2019-06-17 18:03 UTC (permalink / raw) To: Will Deacon Cc: ard.biesheuvel, Catalin Marinas, open list, bcm-kernel-feedback-list, linux-arm-kernel, moderated list:ARM64 PORT (AARCH64 ARCHITECTURE) On 6/17/19 10:32 AM, Will Deacon wrote: > On Thu, Jun 13, 2019 at 07:59:32PM -0700, Florian Fainelli wrote: >> Make ARM64_MODULE_PLTS a selectable Kconfig symbol, since some people >> might have very big modules spilling out of the dedicated module area >> into vmalloc. Help text is copied from the ARM 32-bit counterpart. >> >> Signed-off-by: Florian Fainelli <f.fainelli@gmail.com> >> --- >> arch/arm64/Kconfig | 14 +++++++++++++- >> 1 file changed, 13 insertions(+), 1 deletion(-) >> >> diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig >> index 697ea0510729..36befe987b73 100644 >> --- a/arch/arm64/Kconfig >> +++ b/arch/arm64/Kconfig >> @@ -1418,8 +1418,20 @@ config ARM64_SVE >> KVM in the same kernel image. >> >> config ARM64_MODULE_PLTS >> - bool >> + bool "Use PLTs to allow module memory to spill over into vmalloc area" >> select HAVE_MOD_ARCH_SPECIFIC >> + help >> + Allocate PLTs when loading modules so that jumps and calls whose >> + targets are too far away for their relative offsets to be encoded >> + in the instructions themselves can be bounced via veneers in the >> + module's PLT. This allows modules to be allocated in the generic >> + vmalloc area after the dedicated module memory area has been >> + exhausted. The modules will use slightly more memory, but after >> + rounding up to page size, the actual memory footprint is usually >> + the same. > > Isn't the worry really about the runtime performance overhead introduced > by the veneers, as opposed to the memory usage of the module? The main concern is indeed runtime performance (both added veneers and possibly increased cache trashing) and second could be the increased vmalloc usage. Do you want me to rephrase that part, or drop it? > >> + Disabling this is usually safe for small single-platform >> + configurations. If unsure, say y. > > So should this be on by default? It is turned on under certain conditions that require it (v2 makes that clearer, based on Ard's feedback), having it turned off by default at least makes people realize (or rather can be used as argument) that the modules are possibly too big. Under certain build configurations like test/manufacturing, you might have a set of large modules that should still load, hence this patch. -- Florian _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel ^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [PATCH] arm64: Allow user selection of ARM64_MODULE_PLTS 2019-06-17 18:03 ` Florian Fainelli @ 2019-06-17 18:10 ` Will Deacon 0 siblings, 0 replies; 5+ messages in thread From: Will Deacon @ 2019-06-17 18:10 UTC (permalink / raw) To: Florian Fainelli Cc: ard.biesheuvel, Catalin Marinas, Will Deacon, open list, bcm-kernel-feedback-list, linux-arm-kernel, moderated list:ARM64 PORT (AARCH64 ARCHITECTURE) On Mon, Jun 17, 2019 at 11:03:28AM -0700, Florian Fainelli wrote: > On 6/17/19 10:32 AM, Will Deacon wrote: > > On Thu, Jun 13, 2019 at 07:59:32PM -0700, Florian Fainelli wrote: > >> Make ARM64_MODULE_PLTS a selectable Kconfig symbol, since some people > >> might have very big modules spilling out of the dedicated module area > >> into vmalloc. Help text is copied from the ARM 32-bit counterpart. > >> > >> Signed-off-by: Florian Fainelli <f.fainelli@gmail.com> > >> --- > >> arch/arm64/Kconfig | 14 +++++++++++++- > >> 1 file changed, 13 insertions(+), 1 deletion(-) > >> > >> diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig > >> index 697ea0510729..36befe987b73 100644 > >> --- a/arch/arm64/Kconfig > >> +++ b/arch/arm64/Kconfig > >> @@ -1418,8 +1418,20 @@ config ARM64_SVE > >> KVM in the same kernel image. > >> > >> config ARM64_MODULE_PLTS > >> - bool > >> + bool "Use PLTs to allow module memory to spill over into vmalloc area" > >> select HAVE_MOD_ARCH_SPECIFIC > >> + help > >> + Allocate PLTs when loading modules so that jumps and calls whose > >> + targets are too far away for their relative offsets to be encoded > >> + in the instructions themselves can be bounced via veneers in the > >> + module's PLT. This allows modules to be allocated in the generic > >> + vmalloc area after the dedicated module memory area has been > >> + exhausted. The modules will use slightly more memory, but after > >> + rounding up to page size, the actual memory footprint is usually > >> + the same. > > > > Isn't the worry really about the runtime performance overhead introduced > > by the veneers, as opposed to the memory usage of the module? > > The main concern is indeed runtime performance (both added veneers and > possibly increased cache trashing) and second could be the increased > vmalloc usage. Do you want me to rephrase that part, or drop it? Whichever you prefer. > > > >> + Disabling this is usually safe for small single-platform > >> + configurations. If unsure, say y. > > > > So should this be on by default? > > It is turned on under certain conditions that require it (v2 makes that > clearer, based on Ard's feedback), having it turned off by default at > least makes people realize (or rather can be used as argument) that the > modules are possibly too big. > > Under certain build configurations like test/manufacturing, you might > have a set of large modules that should still load, hence this patch. I'm fine with leaving it default off, but then let's not say "If unsure, say y". In fact, you can remove that whole "disabling this is usually safe" part I reckon. Will _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel ^ permalink raw reply [flat|nested] 5+ messages in thread
end of thread, other threads:[~2019-06-17 18:10 UTC | newest] Thread overview: 5+ messages (download: mbox.gz / follow: Atom feed) -- links below jump to the message on this page -- 2019-06-14 2:59 [PATCH] arm64: Allow user selection of ARM64_MODULE_PLTS Florian Fainelli 2019-06-14 7:02 ` Ard Biesheuvel 2019-06-17 17:32 ` Will Deacon 2019-06-17 18:03 ` Florian Fainelli 2019-06-17 18:10 ` Will Deacon
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