On Thu, 4 Nov 2021 at 14:40, Walter Wu <[email protected]> wrote: > > On Thu, 2021-11-04 at 13:47 +0100, Ard Biesheuvel wrote: > > On Thu, 4 Nov 2021 at 13:31, Walter Wu <[email protected]> > > wrote: > > > > > > On Thu, 2021-11-04 at 09:57 +0100, Ard Biesheuvel wrote: > > > > On Thu, 4 Nov 2021 at 09:53, Christoph Hellwig <[email protected]> > > > > wrote: > > > > > > > > > > On Thu, Nov 04, 2021 at 10:32:21AM +0800, Walter Wu wrote: > > > > > > diff --git a/include/linux/set_memory.h > > > > > > b/include/linux/set_memory.h > > > > > > index f36be5166c19..6c7d1683339c 100644 > > > > > > --- a/include/linux/set_memory.h > > > > > > +++ b/include/linux/set_memory.h > > > > > > @@ -7,11 +7,16 @@ > > > > > > > > > > > > #ifdef CONFIG_ARCH_HAS_SET_MEMORY > > > > > > #include <asm/set_memory.h> > > > > > > + > > > > > > +#ifndef CONFIG_RODATA_FULL_DEFAULT_ENABLED > > > > > > > > > > This is an arm64-specific symbol, and one that only controls a > > > > > default. I don't think it is suitable to key off stubs in > > > > > common > > > > > code. > > > > > > > > > > > +static inline int set_memory_valid(unsigned long addr, int > > > > > > numpages, int enable) { return 0; } > > > > > > > > > > Pleae avoid overly long lines. > > > > > > > > > > > + if > > > > > > (IS_ENABLED(CONFIG_RODATA_FULL_DEFAULT_ENABLED)) > > > > > > { > > > > > > + kaddr = (unsigned > > > > > > long)phys_to_virt(dma_to_phys(dev, *dma_handle)); > > > > > > > > > > This can just use page_address. > > > > > > > > > > > + /* page remove kernel mapping for arm64 > > > > > > */ > > > > > > + set_memory_valid(kaddr, size >> > > > > > > PAGE_SHIFT, > > > > > > 0); > > > > > > + } > > > > > > > > > > But more importantly: set_memory_valid only exists on arm64, > > > > > this > > > > > will break compile everywhere else. And this API is complete > > > > > crap. > > > > > Passing kernel virtual addresses as unsigned long just sucks, > > > > > and > > > > > passing an integer argument for valid/non-valid also is a > > > > > horrible > > > > > API. > > > > > > > > > > > > > ... and as I pointed out before, you can still pass rodata=off on > > > > arm64, and get the old behavior, in which case bad things will > > > > happen > > > > if you try to use an API that expects to operate on page mappings > > > > with > > > > a 1 GB block mapping. > > > > > > > > > > Thanks for your suggestion. > > > > > > > > > > And you still haven't explained what the actual problem is: is > > > > this > > > > about CPU speculation corrupting non-cache coherent inbound DMA? > > > > > > No corrupiton, only cpu read it, we hope to fix the behavior. > > > > > > > Fix which behavior? Please explain > > > > 1) the current behavior > We call dma_direct_alloc() with DMA_ATTR_NO_KERNEL_MAPPING to get the > allocated buffer and the kernel mapping is exist. Our goal is this > buffer doesn't allow to be accessed by cpu. Unfortunately, we see cpu > speculation to read it. So we need to fix it and don't use no-map the > way. > > > 2) why the current behavior is problematic for you > dma_direct_alloc() with DMA_ATTR_NO_KERNEL_MAPPING have kernel mapping, > so it still has cpu speculation read the buffer. Although we have > hardware to protect the buffer, we still hope use software to fix it. >
But *why* is this a problem? You are saying that the speculative accesses are not causing corruption, so they are causing other issues that you want to address. So which issues are we talking about here? > > 3) how this patch changes the current behavior > When call dma_direct_alloc() with DMA_ATTR_NO_KERNEL_MAPPING, then > remove the kernel mapping which belong to the buffer. > > > 4) why the new behavior fixes your problem. > If I understand correctly, want to block cpu speculation, then need > unmap the buffer at stage 1 and stage 2 page table and tlb invalidate. > This patch is to do stage 1 unmap at EL1. > > > > > There is no penalty for using too many words. > > Thanks. > Walter > _______________________________________________ iommu mailing list [email protected] https://lists.linuxfoundation.org/mailman/listinfo/iommu
