From: Peter Zijlstra > Sent: 09 July 2018 15:49 > On Mon, Jul 09, 2018 at 02:33:26PM +0000, Alexey Brodkin wrote: > > > In fact, since alloc_dr() uses kmalloc() to allocate the entire thing, > > > it is impossible to guarantee a larger alignment than kmalloc does. > > > > Well but 4-bytes [which is critical for atomic64_t] should be much less > > than a sane cache line length so above should work. > > AFAICT ARCH_KMALLOC_MINALIGN ends up being 4 on x86_32 (it doesn't > define ARCH_DMA_MINALIGN and doesn't seem to otherwise override the > thing). That seems broken. I wonder what the minimal alignment really is? I suspect some code expects (and gets) 8-byte alignment. The min alignment might even be 16 or 32 bytes. There aren't many x86 instructions that fault on mis-aligned addresses, but there are a few. Mostly related to the fpu - probably including the fpu save area. David
