Messages in this thread Patch in this message | | | Date | Tue, 10 Jan 2023 17:05:06 +0200 | Subject | Re: [PATCH] lib/scatterlist: Fix to calculate the last_pg properly | From | Yishai Hadas <> |
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On 10/01/2023 15:53, Jason Gunthorpe wrote: > On Tue, Jan 10, 2023 at 10:01:53AM +0200, Yishai Hadas wrote: >> On 10/01/2023 7:08, Matthew Wilcox wrote: >>> On Mon, Jan 09, 2023 at 04:47:01PM +0200, Yishai Hadas wrote: >>>> if (sgt_append->prv) { >>>> + unsigned long paddr = >>>> + (page_to_pfn(sg_page(sgt_append->prv)) * PAGE_SIZE + >>> 1. page_to_pfn() * PAGE_SIZE is spelled page_to_phys() >>> >>> 2. physical addresses have type phys_addr_t. Oh, wait, paddr isn't a >>> physical address, it's a pfn because you divide by PAGE_SIZE at the end. >>> But you will get truncation on 32-bit, because page_to_pfn() has type >>> unsigned long. Anyway, this shouldn't be called paddr. Maybe last_pfn >>> or something? >>> >>>> + sgt_append->prv->offset + sgt_append->prv->length) / >>>> + PAGE_SIZE; >> In this area of the patch I just reverted to what we had in 6.1 [1] where we >> were good. >> >> I can send V1 and replace the 'paddr' to be called 'last_pfn' if it's really >> needed. > Please change it as Matthew describes so it is clearer > > Jason
OK
Once cleaning the code and renaming to 'last_pfn', could also see that we had to use below '- 1' instead of '- PAGE_SIZE'.
The expected diff compared to V0 can be seen below.
Will repeat some testing and send V1 once be ready.
+++ b/lib/scatterlist.c @@ -470,18 +470,16 @@ int sg_alloc_append_table_from_pages(struct sg_append_table *sgt_append, return -EOPNOTSUPP;
if (sgt_append->prv) { - unsigned long paddr = - (page_to_pfn(sg_page(sgt_append->prv)) * PAGE_SIZE + - sgt_append->prv->offset + sgt_append->prv->length) / - PAGE_SIZE; + unsigned long last_pfn = (page_to_phys(sg_page(sgt_append->prv)) + + sgt_append->prv->offset + sgt_append->prv->length) / PAGE_SIZE;
if (WARN_ON(offset)) return -EINVAL;
/* Merge contiguous pages into the last SG */ prv_len = sgt_append->prv->length; - if (page_to_pfn(pages[0]) == paddr) { - last_pg = pfn_to_page(paddr - PAGE_SIZE); + if (page_to_pfn(pages[0]) == last_pfn) { + last_pg = pfn_to_page(last_pfn - 1); while (n_pages && pages_are_mergeable(pages[0], last_pg)) { if (sgt_append->prv->length + PAGE_SIZE > max_segment) break; Yishai
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