On Thu, 24 Oct 2024, Ryan Roberts wrote: > 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. You are right. It would be nice to add a in-code comment to explain this. Reviewed-by: Stefano Stabellini <sstabellini@xxxxxxxxxx> > >>> /* 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) > >> >
