On Mon, Jun 17, 2019 at 03:29:59PM -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 and > modified to a mention of KASLR and specific ARM errata workaround(s). > > Signed-off-by: Florian Fainelli <f.faine...@gmail.com> > --- > Changes in v3: > - take out the part about "The modules will use slightly more memory, but > after > rounding up to page size, the actual memory footprint is usually the same. > - take out the "If unusure say Y", since we would really prefer this to > be off by default for maximum performance > > Changes in v2: > > - added Ard's paragraph about KASLR > - added a paragraph about specific workarounds also requiring > ARM64_MODULE_PLTS > > arch/arm64/Kconfig | 20 +++++++++++++++++++- > 1 file changed, 19 insertions(+), 1 deletion(-) > > diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig > index 697ea0510729..9206feaeff07 100644 > --- a/arch/arm64/Kconfig > +++ b/arch/arm64/Kconfig > @@ -1418,8 +1418,26 @@ 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. > + > + 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. > + > + Specific errata workaround(s) might also force module PLTs to be > + enabled (ARM64_ERRATUM_843419). > + > + Disabling this is usually safe for small single-platform > + configurations.
I think I'd still drop this last sentence, because labelling a kernel "usually safe" without this option is a bit OTT. We'll just reject large modules, nothing unsafe about that. Assuming Catalin can do that when he applies, so: Acked-by: Will Deacon <will.dea...@arm.com> Will
