On Fri, Jun 18, 2021 at 11:37:28AM +0800, Herbert Xu wrote: > On Thu, Jun 17, 2021 at 08:01:57PM -0700, Ira Weiny wrote: > > > > > + flush_kernel_dcache_page(__page); \ > > > > Is this required on 32bit systems? Why is kunmap_flush_on_unmap() not > > sufficient on 64bit systems? The normal kunmap_local() path does that. > > > > I'm sorry but I did not see a conclusion to my query on V1. Herbert implied the > > he just copied from the crypto code.[1] I'm concerned that this _dirty() call > > is just going to confuse the users of kmap even more. So why can't we get to > > the bottom of why flush_kernel_dcache_page() needs so much logic around it > > before complicating the general kernel users. > > > > I would like to see it go away if possible. > > This thread may be related: > > https://lwn.net/Articles/240249/ Interesting! Thanks! Digging around a bit more I found: https://lore.kernel.org/patchwork/patch/439637/ Auditing all the flush_dcache_page() arch code reveals that the mapping field is either unused, or is checked for NULL. Furthermore, all the implementations call page_mapping_file() which further limits the page to not be a swap page. All flush_kernel_dcache_page() implementations appears to operate the same way in all arch's which define that call. So I'm confident now that additional !PageSlab(__page) checks are not needed and this patch is unnecessary. Christoph, can we leave this out of the kmap API and just fold the flush_kernel_dcache_page() calls back into the bvec code? Unfortunately, I'm not convinced this can be handled completely by kunmap_local() nor the mem*_page() calls because there is a difference between flush_dcache_page() and flush_kernel_dcache_page() in most archs... [parisc being an exception which falls back to flush_kernel_dcache_page()]... It seems like the generic unmap path _should_ be able to determine which call to make based on the page but I'd have to look at that more. Ira
