On Mon, Apr 20, 2026 at 05:18:10PM +0000, Michael Kelley wrote: > From: Stanislav Kinsburskii <[email protected]> Sent: Monday, > April 20, 2026 9:22 AM > > > > On Mon, Apr 13, 2026 at 09:08:16PM +0000, Michael Kelley wrote: > > > From: Stanislav Kinsburskii <[email protected]> Sent: > > > Monday, March 30, 2026 1:04 PM > > > > > > [snip] > > > > > @@ -57,60 +58,61 @@ static int mshv_chunk_stride(struct page *page, > > > > /** > > > > * mshv_region_process_chunk - Processes a contiguous chunk of memory > > > > pages > > > > * in a region. > > > > - * @region : Pointer to the memory region structure. > > > > - * @flags : Flags to pass to the handler. > > > > - * @page_offset: Offset into the region's pages array to start > > > > processing. > > > > - * @page_count : Number of pages to process. > > > > - * @handler : Callback function to handle the chunk. > > > > + * @region : Pointer to the memory region structure. > > > > + * @flags : Flags to pass to the handler. > > > > + * @pfn_offset: Offset into the region's PFNs array to start > > > > processing. > > > > + * @pfn_count : Number of PFNs to process. > > > > + * @handler : Callback function to handle the chunk. > > > > * > > > > - * This function scans the region's pages starting from @page_offset, > > > > - * checking for contiguous present pages of the same size (normal or > > > > huge). > > > > - * It invokes @handler for the chunk of contiguous pages found. > > > > Returns the > > > > - * number of pages handled, or a negative error code if the first page > > > > is > > > > - * not present or the handler fails. > > > > + * This function scans the region's PFNs starting from @pfn_offset, > > > > + * checking for contiguous valid PFNs backed by pages of the same size > > > > + * (normal or huge). It invokes @handler for the chunk of contiguous > > > > valid > > > > + * PFNs found. Returns the number of PFNs handled, or a negative error > > > > code > > > > + * if the first PFN is invalid or the handler fails. > > > > * > > > > - * Note: The @handler callback must be able to handle both normal and > > > > huge > > > > - * pages. > > > > + * Note: The @handler callback must be able to handle valid PFNs > > > > backed by > > > > + * both normal and huge pages. > > > > * > > > > * Return: Number of pages handled, or negative error code. > > > > */ > > > > -static long mshv_region_process_chunk(struct mshv_mem_region *region, > > > > - u32 flags, > > > > - u64 page_offset, u64 page_count, > > > > - int (*handler)(struct > > > > mshv_mem_region *region, > > > > - u32 flags, > > > > - u64 page_offset, > > > > - u64 page_count, > > > > - bool huge_page)) > > > > +static long mshv_region_process_pfns(struct mshv_mem_region *region, > > > > + u32 flags, > > > > + u64 pfn_offset, u64 pfn_count, > > > > + int (*handler)(struct > > > > mshv_mem_region *region, > > > > + u32 flags, > > > > + u64 pfn_offset, > > > > + u64 pfn_count, > > > > + bool huge_page)) > > > > { > > > > - u64 gfn = region->start_gfn + page_offset; > > > > + u64 gfn = region->start_gfn + pfn_offset; > > > > u64 count; > > > > - struct page *page; > > > > + unsigned long pfn; > > > > int stride, ret; > > > > > > > > - page = region->mreg_pages[page_offset]; > > > > - if (!page) > > > > + pfn = region->mreg_pfns[pfn_offset]; > > > > + if (!pfn_valid(pfn)) > > > > return -EINVAL; > > > > > > > > - stride = mshv_chunk_stride(page, gfn, page_count); > > > > + stride = mshv_chunk_stride(pfn_to_page(pfn), gfn, pfn_count); > > > > if (stride < 0) > > > > return stride; > > > > > > > > /* Start at stride since the first stride is validated */ > > > > - for (count = stride; count < page_count; count += stride) { > > > > - page = region->mreg_pages[page_offset + count]; > > > > + for (count = stride; count < pfn_count ; count += stride) { > > > > + pfn = region->mreg_pfns[pfn_offset + count]; > > > > > > > > - /* Break if current page is not present */ > > > > - if (!page) > > > > + /* Break if current pfn is invalid */ > > > > + if (!pfn_valid(pfn)) > > > > > > pfn_valid() is a relatively expensive test to be doing in a loop > > > on what may be every single page. It does an RCU lock/unlock > > > and make other checks that aren't necessary here. Since > > > mreg_pfns[] is populated from mm calls, the only invalid PFNs > > > would be MSHV_INVALID_PFN that code in this module has > > > explicitly put there. Just testing against MSHV_INVALID_PFN > > > would be a lot faster here and elsewhere in this module. It's > > > really a "pfn set/not set" test. Defining a pfn_set() macro > > > here in this module that tests against MSHV_INVALID_PFN > > > would accomplish the same thing more efficiently. > > > > > > > Yes, we could do it the way you suggest. For completeness, I should add > > that pfn_valid() is expensive only on 32-bit ARM and ARC, which we > > don’t care about. > > > > Could you elaborate? On x86, I'm seeing that pfn_valid() is about > 220 bytes of code. It's the version in include/linux/mmzone.h, not > the simple version in include/asm-generic/memory_model.h. The > latter is used only for CONFIG_FLATMEM=y. Or is the root partition > kernel build setting CONFIG_FLATMEM_MANUAL and hence getting > the simple version? >
I was wrong: this long function is indeed compiled for x86. Still, it's not big of a runtime impact as taking the rcu lock is cheap, but I'll simplify as proposed. Thanks, Stanislav > Michael
