On Wed, Dec 02, 2015 at 09:37:05AM +0100, Arnd Bergmann wrote: > On Wednesday 02 December 2015 02:35:03 Yury Norov wrote: > > On Tue, Dec 01, 2015 at 11:39:42PM +0100, Arnd Bergmann wrote: > > > On Wednesday 02 December 2015 00:29:04 Yury Norov wrote: > > > I'm not sure I understand this part. What changes specifically do we need? > > > > > > > For kernel: > > > > diff --git a/arch/arm64/include/asm/shmparam.h > > b/arch/arm64/include/asm/shmparam.h > > index 4df608a..e368a55 100644 > > --- a/arch/arm64/include/asm/shmparam.h > > +++ b/arch/arm64/include/asm/shmparam.h > > @@ -21,7 +21,7 @@ > > * alignment value. Since we don't have aliasing D-caches, the > > rest of > > * the time we can safely use PAGE_SIZE. > > */ > > -#define COMPAT_SHMLBA 0x4000 > > +#define COMPAT_SHMLBA (4 * PAGE_SIZE) > > > > #include <asm-generic/shmparam.h> > > > > diff --git a/arch/arm64/kernel/sys_ilp32.c > > b/arch/arm64/kernel/sys_ilp32.c > > index c5bc712..877bedf 100644 > > --- a/arch/arm64/kernel/sys_ilp32.c > > +++ b/arch/arm64/kernel/sys_ilp32.c > > @@ -42,15 +42,12 @@ asmlinkage long sys_rt_sigreturn_wrapper(void); > > #define compat_sys_pwrite64 sys_pwrite64 > > #define compat_sys_readahead sys_readahead > > #define compat_sys_rt_sigaction sys_rt_sigaction > > -#define compat_sys_shmat sys_shmat > > #define compat_sys_sync_file_range sys_sync_file_range > > #define compat_sys_truncate64 sys_truncate > > #define compat_sys_sigaltstack sys_sigaltstack > > > > For library - just create a header in ilp32 directory that defines > > SHMLBA exactly as arm: __getpagesize () << 2 > > I think we both reversed our positions here ;-) > > The 4*PAGE_SIZE on ARM is an architecture specific oddity, I believe > to work around aliasing caches on ARMv6. As no other architecture does > this, we're probably better off not duplicating it for aarch64-ilp32 > and just use sys_shmat as your v6 patch does. > > > > It sounds like shmat is one of the cases we an override makes sense > > > and we should use sys_shmat with PAGE_SIZE for aarch64 ilp32 mode. > > > > > > > [...] > > > > > We normally assume that the page size on ARM is fixed to 4K, so > > > there might be user space that just hardcodes 16K SHMLBA > > > > It means that we should use compat_sys_shmat because hardcoded > > userspace may have a chance to work for 4K pages. If we'll use > > sys_shmat (and so 4K SHMLBA), we'll definitely make hardcoded > > userspace broken. Non-hardcoded userspace will work anyway. > > > > We can describe in documentation that 4k pages are prefferable. > > The hardcoded user space would only apply to old source code that > specifically tries to adapt to what ARM does, but gets it wrong, > If we have source code that is converted from x86 or mips and > hardcodes anything, it's more likely to be the normal __getpagesize(). > > Arnd
Hmm... OK. Let's have non-compat shmat here... -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
