On 23/10/2024 02:23, Stefano Stabellini wrote: > +Julien > > On Wed, 16 Oct 2024, Ryan Roberts wrote: >> + Juergen Gross, Stefano Stabellini >> >> This was a rather tricky series to get the recipients correct for and my script >> did not realize that "supporter" was a pseudonym for "maintainer" so you were >> missed off the original post. Appologies! >> >> More context in cover letter: >> https://lore.kernel.org/all/20241014105514.3206191-1-ryan.roberts@xxxxxxx/ >> >> >> On 14/10/2024 11:58, Ryan Roberts wrote: >>> To prepare for supporting boot-time page size selection, refactor code >>> to remove assumptions about PAGE_SIZE being compile-time constant. Code >>> intended to be equivalent when compile-time page size is active. >>> >>> Allocate enough "frame_list" static storage in the balloon driver for >>> the maximum supported page size. Although continue to use only the first >>> PAGE_SIZE of the buffer at run-time to maintain existing behaviour. >>> >>> Refactor xen_biovec_phys_mergeable() to convert ifdeffery to c if/else. >>> For compile-time page size, the compiler will choose one branch and >>> strip the dead one. For boot-time, it can be evaluated at run time. >>> >>> Refactor a BUILD_BUG_ON to evaluate the limit (when the minimum >>> supported page size is selected at boot-time). >>> >>> Reserve enough storage for max page size in "struct remap_data" and >>> "struct xenbus_map_node". >>> >>> Signed-off-by: Ryan Roberts <ryan.roberts@xxxxxxx> >>> --- >>> >>> ***NOTE*** >>> Any confused maintainers may want to read the cover note here for context: >>> https://lore.kernel.org/all/20241014105514.3206191-1-ryan.roberts@xxxxxxx/ >>> >>> drivers/xen/balloon.c | 11 ++++++----- >>> drivers/xen/biomerge.c | 12 ++++++------ >>> drivers/xen/privcmd.c | 2 +- >>> drivers/xen/xenbus/xenbus_client.c | 5 +++-- >>> drivers/xen/xlate_mmu.c | 6 +++--- >>> include/xen/page.h | 2 ++ >>> 6 files changed, 21 insertions(+), 17 deletions(-) >>> >>> diff --git a/drivers/xen/balloon.c b/drivers/xen/balloon.c >>> index 528395133b4f8..0ed5f6453af0e 100644 >>> --- a/drivers/xen/balloon.c >>> +++ b/drivers/xen/balloon.c >>> @@ -131,7 +131,8 @@ struct balloon_stats balloon_stats; >>> EXPORT_SYMBOL_GPL(balloon_stats); >>> >>> /* We increase/decrease in batches which fit in a page */ >>> -static xen_pfn_t frame_list[PAGE_SIZE / sizeof(xen_pfn_t)]; >>> +static xen_pfn_t frame_list[PAGE_SIZE_MAX / sizeof(xen_pfn_t)]; >>> +#define FRAME_LIST_NR_ENTRIES (PAGE_SIZE / sizeof(xen_pfn_t)) >>> >>> >>> /* List of ballooned pages, threaded through the mem_map array. */ >>> @@ -389,8 +390,8 @@ static enum bp_state increase_reservation(unsigned long nr_pages) >>> unsigned long i; >>> struct page *page; >>> >>> - if (nr_pages > ARRAY_SIZE(frame_list)) >>> - nr_pages = ARRAY_SIZE(frame_list); >>> + if (nr_pages > FRAME_LIST_NR_ENTRIES) >>> + nr_pages = FRAME_LIST_NR_ENTRIES; >>> >>> page = list_first_entry_or_null(&ballooned_pages, struct page, lru); >>> for (i = 0; i < nr_pages; i++) { >>> @@ -434,8 +435,8 @@ static enum bp_state decrease_reservation(unsigned long nr_pages, gfp_t gfp) >>> int ret; >>> LIST_HEAD(pages); >>> >>> - if (nr_pages > ARRAY_SIZE(frame_list)) >>> - nr_pages = ARRAY_SIZE(frame_list); >>> + if (nr_pages > FRAME_LIST_NR_ENTRIES) >>> + nr_pages = FRAME_LIST_NR_ENTRIES; >>> >>> for (i = 0; i < nr_pages; i++) { >>> page = alloc_page(gfp); >>> diff --git a/drivers/xen/biomerge.c b/drivers/xen/biomerge.c >>> index 05a286d24f148..28f0887e40026 100644 >>> --- a/drivers/xen/biomerge.c >>> +++ b/drivers/xen/biomerge.c >>> @@ -8,16 +8,16 @@ >>> bool xen_biovec_phys_mergeable(const struct bio_vec *vec1, >>> const struct page *page) >>> { >>> -#if XEN_PAGE_SIZE == PAGE_SIZE >>> - unsigned long bfn1 = pfn_to_bfn(page_to_pfn(vec1->bv_page)); >>> - unsigned long bfn2 = pfn_to_bfn(page_to_pfn(page)); >>> + if (XEN_PAGE_SIZE == PAGE_SIZE) { >>> + unsigned long bfn1 = pfn_to_bfn(page_to_pfn(vec1->bv_page)); >>> + unsigned long bfn2 = pfn_to_bfn(page_to_pfn(page)); >>> + >>> + return bfn1 + PFN_DOWN(vec1->bv_offset + vec1->bv_len) == bfn2; >>> + } >>> >>> - return bfn1 + PFN_DOWN(vec1->bv_offset + vec1->bv_len) == bfn2; >>> -#else >>> /* >>> * XXX: Add support for merging bio_vec when using different page >>> * size in Xen and Linux. >>> */ >>> return false; >>> -#endif >>> } >>> diff --git a/drivers/xen/privcmd.c b/drivers/xen/privcmd.c >>> index 9563650dfbafc..847f7b806caf7 100644 >>> --- a/drivers/xen/privcmd.c >>> +++ b/drivers/xen/privcmd.c >>> @@ -557,7 +557,7 @@ static long privcmd_ioctl_mmap_batch( >>> state.global_error = 0; >>> state.version = version; >>> >>> - BUILD_BUG_ON(((PAGE_SIZE / sizeof(xen_pfn_t)) % XEN_PFN_PER_PAGE) != 0); >>> + BUILD_BUG_ON(((PAGE_SIZE_MIN / sizeof(xen_pfn_t)) % XEN_PFN_PER_PAGE_MAX) != 0); > > Is there any value in keep this test? And if so, what should it look > like? I think we should turn it into a WARN_ON: > > WARN_ON(((PAGE_SIZE / sizeof(xen_pfn_t)) % XEN_PFN_PER_PAGE) != 0); > > It doesn't make much sense having a BUILD_BUG_ON on a variable that can > change? I believe that as long as we assume sizeof(xen_pfn_t), PAGE_SIZE and XEN_PAGE_SIZE are all power-of-two sizes, then this single build-time test should cover all possible boot-time PAGE_SIZEs. Logic: If PAGE_SIZE and XEN_PAGE_SIZE are power-of-two, then XEN_PFN_PER_PAGE must also be power-of-two. XEN_PFN_PER_PAGE_MAX is just the worst case limit. (PAGE_SIZE_MIN / sizeof(xen_pfn_t)) is the number of xen_pfn_t that fit on smallest page. If you can get an integer multiple number of XEN_PFN_PER_PAGE_MAX on the smallest page, then it remains an integer multiple as PAGE_SIZE gets bigger, assuming it is restricted to power-of-two sizes. Perhaps there is a floor in my logic? I'd prefer to keep BUILD_BUG_ON where possible to avoid the additional image size bloat and runtime costs. Thanks, Ryan > > >>> /* mmap_batch_fn guarantees ret == 0 */ >>> BUG_ON(traverse_pages_block(m.num, sizeof(xen_pfn_t), >>> &pagelist, mmap_batch_fn, &state)); >>> diff --git a/drivers/xen/xenbus/xenbus_client.c b/drivers/xen/xenbus/xenbus_client.c >>> index 51b3124b0d56c..99bde836c10c4 100644 >>> --- a/drivers/xen/xenbus/xenbus_client.c >>> +++ b/drivers/xen/xenbus/xenbus_client.c >>> @@ -49,9 +49,10 @@ >>> >>> #include "xenbus.h" >>> >>> -#define XENBUS_PAGES(_grants) (DIV_ROUND_UP(_grants, XEN_PFN_PER_PAGE)) >>> +#define XENBUS_PAGES(_grants) (DIV_ROUND_UP(_grants, XEN_PFN_PER_PAGE)) >>> +#define XENBUS_PAGES_MAX(_grants) (DIV_ROUND_UP(_grants, XEN_PFN_PER_PAGE_MIN)) >>> >>> -#define XENBUS_MAX_RING_PAGES (XENBUS_PAGES(XENBUS_MAX_RING_GRANTS)) >>> +#define XENBUS_MAX_RING_PAGES (XENBUS_PAGES_MAX(XENBUS_MAX_RING_GRANTS)) >>> >>> struct xenbus_map_node { >>> struct list_head next; >>> diff --git a/drivers/xen/xlate_mmu.c b/drivers/xen/xlate_mmu.c >>> index f17c4c03db30c..a757c801a7542 100644 >>> --- a/drivers/xen/xlate_mmu.c >>> +++ b/drivers/xen/xlate_mmu.c >>> @@ -74,9 +74,9 @@ struct remap_data { >>> int mapped; >>> >>> /* Hypercall parameters */ >>> - int h_errs[XEN_PFN_PER_PAGE]; >>> - xen_ulong_t h_idxs[XEN_PFN_PER_PAGE]; >>> - xen_pfn_t h_gpfns[XEN_PFN_PER_PAGE]; >>> + int h_errs[XEN_PFN_PER_PAGE_MAX]; >>> + xen_ulong_t h_idxs[XEN_PFN_PER_PAGE_MAX]; >>> + xen_pfn_t h_gpfns[XEN_PFN_PER_PAGE_MAX]; >>> >>> int h_iter; /* Iterator */ >>> }; >>> diff --git a/include/xen/page.h b/include/xen/page.h >>> index 285677b42943a..86683a30038a3 100644 >>> --- a/include/xen/page.h >>> +++ b/include/xen/page.h >>> @@ -21,6 +21,8 @@ >>> ((page_to_pfn(page)) << (PAGE_SHIFT - XEN_PAGE_SHIFT)) >>> >>> #define XEN_PFN_PER_PAGE (PAGE_SIZE / XEN_PAGE_SIZE) >>> +#define XEN_PFN_PER_PAGE_MIN (PAGE_SIZE_MIN / XEN_PAGE_SIZE) >>> +#define XEN_PFN_PER_PAGE_MAX (PAGE_SIZE_MAX / XEN_PAGE_SIZE) >>> >>> #define XEN_PFN_DOWN(x) ((x) >> XEN_PAGE_SHIFT) >>> #define XEN_PFN_UP(x) (((x) + XEN_PAGE_SIZE-1) >> XEN_PAGE_SHIFT) >>
