Re: [PATCH v1 08/16] kmsan: convert kmsan_handle_dma to use physical addresses

[Leon Romanovsky <leon@xxxxxxxxxx>]

On Thu, Aug 07, 2025 at 09:21:15AM -0300, Jason Gunthorpe wrote:
> On Mon, Aug 04, 2025 at 03:42:42PM +0300, Leon Romanovsky wrote:
> > From: Leon Romanovsky <leonro@xxxxxxxxxx>
> > 
> > Convert the KMSAN DMA handling function from page-based to physical
> > address-based interface.
> > 
> > The refactoring renames kmsan_handle_dma() parameters from accepting
> > (struct page *page, size_t offset, size_t size) to (phys_addr_t phys,
> > size_t size). A PFN_VALID check is added to prevent KMSAN operations
> > on non-page memory, preventing from non struct page backed address,
> > 
> > As part of this change, support for highmem addresses is implemented
> > using kmap_local_page() to handle both lowmem and highmem regions
> > properly. All callers throughout the codebase are updated to use the
> > new phys_addr_t based interface.
> 
> Use the function Matthew pointed at kmap_local_pfn()
> 
> Maybe introduce the kmap_local_phys() he suggested too.

At this point it gives nothing.

> 
> >  /* Helper function to handle DMA data transfers. */
> > -void kmsan_handle_dma(struct page *page, size_t offset, size_t size,
> > +void kmsan_handle_dma(phys_addr_t phys, size_t size,
> >                   enum dma_data_direction dir)
> >  {
> >     u64 page_offset, to_go, addr;
> > +   struct page *page;
> > +   void *kaddr;
> >  
> > -   if (PageHighMem(page))
> > +   if (!pfn_valid(PHYS_PFN(phys)))
> >             return;
> 
> Not needed, the caller must pass in a phys that is kmap
> compatible. Maybe just leave a comment. FWIW today this is also not
> checking for P2P or DEVICE non-kmap struct pages either, so it should
> be fine without checks.

It is not true as we will call to kmsan_handle_dma() unconditionally in
dma_map_phys(). The reason to it is that kmsan_handle_dma() is guarded
with debug kconfig options and cost of pfn_valid() can be accommodated
in that case. It gives more clean DMA code.

   155 dma_addr_t dma_map_phys(struct device *dev, phys_addr_t phys, size_t 
size,
   156                 enum dma_data_direction dir, unsigned long attrs)
   157 {
   <...>
   187
   188         kmsan_handle_dma(phys, size, dir);
   189         trace_dma_map_phys(dev, phys, addr, size, dir, attrs);
   190         debug_dma_map_phys(dev, phys, size, dir, addr, attrs);
   191
   192         return addr;
   193 }
   194 EXPORT_SYMBOL_GPL(dma_map_phys);

So let's keep this patch as is.

Thanks