Hei hei, I would like to kindly ask about the status of this patch.
On Wed, Apr 15, 2020 at 04:35:21PM +0200, Alexander Dahl wrote: > now after v5.7-rc1 is out, I would kindly ask, if anyone had time to > review this one line patch? Is anything wrong with that fix? Did it maybe not reach the right maintainers? I used scripts/get_maintainer.pl to get my recipient list. > (I added the current fli4l kernel package maintainer Florian to Cc to > let him know I'm still having an eye on this.) > > Greets > Alex > > On Sat, Mar 21, 2020 at 07:28:23PM +0100, Alexander Dahl wrote: > > For ARCH=x86 (32 bit) when you set CONFIG_IOMMU_INTEL since c5a5dc4cbbf4 > > ("iommu/vt-d: Don't switch off swiotlb if bounce page is used") there's > > a dependency on CONFIG_SWIOTLB, which was not necessarily active before. > > > > The init code for swiotlb in 'pci_swiotlb_detect_4gb()' compares > > something against MAX_DMA32_PFN to decide if it should be active. > > However that define suffers from an arithmetic overflow since > > 1b7e03ef7570 ("x86, NUMA: Enable emulation on 32bit too") when it was > > first made visible to x86_32. > > > > The effect is at boot time 64 MiB (default size) were allocated for > > bounce buffers now, which is a noticeable amount of memory on small > > systems. We noticed this effect on the fli4l Linux distribution when > > migrating from kernel v4.19 (LTS) to v5.4 (LTS) on boards like pcengines > > ALIX 2D3 with 256 MiB memory for example: > > > > Linux version 5.4.22 (buildroot@buildroot) (gcc version 7.3.0 (Buildroot > > 2018.02.8)) #1 SMP Mon Nov 26 23:40:00 CET 2018 > > … > > Memory: 183484K/261756K available (4594K kernel code, 393K rwdata, 1660K > > rodata, 536K init, 456K bss , 78272K reserved, 0K cma-reserved, 0K highmem) > > … > > PCI-DMA: Using software bounce buffering for IO (SWIOTLB) > > software IO TLB: mapped [mem 0x0bb78000-0x0fb78000] (64MB) > > > > The initial analysis and the suggested fix was done by user 'sourcejedi' > > at stackoverflow and explicitly marked as GPLv2 for inclusion in the > > Linux kernel: > > > > https://unix.stackexchange.com/a/520525/50007 > > > > The actual calculation however is the same as for arch/mips now as > > suggested by Robin Murphy. > > > > Fixes: https://web.nettworks.org/bugs/browse/FFL-2560 > > Fixes: https://unix.stackexchange.com/q/520065/50007 > > Reported-by: Alan Jenkins <alan.christopher.jenk...@gmail.com> > > Suggested-by: Robin Murphy <robin.mur...@arm.com> > > Signed-off-by: Alexander Dahl <p...@lespocky.de> > > --- > > > > Notes: > > v1 -> v2: > > - use the same calculation as with arch/mips (Robin Murphy) > > > > arch/x86/include/asm/dma.h | 2 +- > > 1 file changed, 1 insertion(+), 1 deletion(-) > > > > diff --git a/arch/x86/include/asm/dma.h b/arch/x86/include/asm/dma.h > > index 00f7cf45e699..8e95aa4b0d17 100644 > > --- a/arch/x86/include/asm/dma.h > > +++ b/arch/x86/include/asm/dma.h > > @@ -74,7 +74,7 @@ > > #define MAX_DMA_PFN ((16UL * 1024 * 1024) >> PAGE_SHIFT) > > > > /* 4GB broken PCI/AGP hardware bus master zone */ > > -#define MAX_DMA32_PFN ((4UL * 1024 * 1024 * 1024) >> PAGE_SHIFT) > > +#define MAX_DMA32_PFN (1UL << (32 - PAGE_SHIFT)) > > > > #ifdef CONFIG_X86_32 > > /* The maximum address that we can perform a DMA transfer to on this > > platform */ > > -- > > 2.20.1 Greets Alex -- /"\ ASCII RIBBON | »With the first link, the chain is forged. The first \ / CAMPAIGN | speech censured, the first thought forbidden, the X AGAINST | first freedom denied, chains us all irrevocably.« / \ HTML MAIL | (Jean-Luc Picard, quoting Judge Aaron Satie)
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