On Wed, Apr 04, 2018 at 10:48:31PM +1000, Michael Ellerman wrote: > Anshuman Khandual <[email protected]> writes: > > Even though SWIOTLB slab gets allocated and initialized on powerpc with > > swiotlb_init() called during mem_init(), it gets released away again on > > POWER platform because 'ppc_swiotlb_enable' never gets set. The function > > swiotlb_detect_4g() checks for 4GB memory and then sets the variable > > 'ppc_swiotlb_enable' which prevents freeing up the SWIOTLB slab. Lets > > make POWER platform call swiotlb_detect_4g() during setup_arch() which > > will keep the SWIOTLB slab through out the runtime. > > > > A previous commit cf5621032f ("powerpc/64: Limit ZONE_DMA32 to 4GiB in > > swiotlb_detect_4g()") enforced 4GB limit on ZONE_DMA32 which is is not > > applicable on POWER (CONFIG_PPC_BOOK3S_64) platform. Lets remove this > > unnecessary restriction. > > You're using "POWER" to mean Book3S 64-bit, but "POWER" is something > else (the ISA for POWER1/POWER2). > > So please just say "Book3S 64-bit" or talk about a specific CPU, eg. > Power9. > > > After the patch, SWIOTLB slab does not get released. > > > > [0.410992] software IO TLB [mem 0xfbff0000-0xffff0000] (64MB) mapped > > at [00000000767f6cb3-000000004a10114f] > > But we don't want SWIOTLB on any existing Book3S 64-bit platforms, so > leaving it enabled is just wasting memory. > > > diff --git a/arch/powerpc/kernel/setup-common.c > > b/arch/powerpc/kernel/setup-common.c > > index d73ec518ef80..c4db844e0b0d 100644 > > --- a/arch/powerpc/kernel/setup-common.c > > +++ b/arch/powerpc/kernel/setup-common.c > > @@ -944,6 +944,7 @@ void __init setup_arch(char **cmdline_p) > > /* Initialize the MMU context management stuff. */ > > mmu_context_init(); > > > > + swiotlb_detect_4g(); > > You shouldn't be calling this, your use case has nothing to do with 4GB. > > Instead when you detect that you're running under the ultravisor then > you should set ppc_swiotlb_enable = 1.
Please assume that you will have a interface to detect if you are running in a protected-environment(AKA secure-environment). So maybe you can rename swiotlb_detect_4g() to swiotlb_detect() and modify that function to enable or disable ppc_swiotlb_enable depending on the availability of 4g or availability of protected-environment? RP
