Messages in this thread Patch in this message | | | Subject | Re: [PATCH 3/8] xen/grant-table: Allow allocating buffers suitable for DMA | From | Oleksandr Andrushchenko <> | Date | Wed, 30 May 2018 09:34:44 +0300 |
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On 05/29/2018 10:10 PM, Boris Ostrovsky wrote: > On 05/25/2018 11:33 AM, Oleksandr Andrushchenko wrote: >> From: Oleksandr Andrushchenko <oleksandr_andrushchenko@epam.com> >> >> Extend grant table module API to allow allocating buffers that can >> be used for DMA operations and mapping foreign grant references >> on top of those. >> The resulting buffer is similar to the one allocated by the balloon >> driver in terms that proper memory reservation is made >> ({increase|decrease}_reservation and VA mappings updated if needed). >> This is useful for sharing foreign buffers with HW drivers which >> cannot work with scattered buffers provided by the balloon driver, >> but require DMAable memory instead. >> >> Signed-off-by: Oleksandr Andrushchenko <oleksandr_andrushchenko@epam.com> >> --- >> drivers/xen/Kconfig | 13 ++++ >> drivers/xen/grant-table.c | 124 ++++++++++++++++++++++++++++++++++++++ >> include/xen/grant_table.h | 25 ++++++++ >> 3 files changed, 162 insertions(+) >> >> diff --git a/drivers/xen/Kconfig b/drivers/xen/Kconfig >> index e5d0c28372ea..3431fe210624 100644 >> --- a/drivers/xen/Kconfig >> +++ b/drivers/xen/Kconfig >> @@ -161,6 +161,19 @@ config XEN_GRANT_DEV_ALLOC >> to other domains. This can be used to implement frontend drivers >> or as part of an inter-domain shared memory channel. >> >> +config XEN_GRANT_DMA_ALLOC >> + bool "Allow allocating DMA capable buffers with grant reference module" >> + depends on XEN > > Should it depend on anything from DMA? CONFIG_HAS_DMA for example? Yes, it must be "depends on XEN && HAS_DMA", thank you > >> + help >> + Extends grant table module API to allow allocating DMA capable >> + buffers and mapping foreign grant references on top of it. >> + The resulting buffer is similar to one allocated by the balloon >> + driver in terms that proper memory reservation is made >> + ({increase|decrease}_reservation and VA mappings updated if needed). >> + This is useful for sharing foreign buffers with HW drivers which >> + cannot work with scattered buffers provided by the balloon driver, >> + but require DMAable memory instead. >> + >> config SWIOTLB_XEN >> def_bool y >> select SWIOTLB >> diff --git a/drivers/xen/grant-table.c b/drivers/xen/grant-table.c >> index d7488226e1f2..06fe6e7f639c 100644 >> --- a/drivers/xen/grant-table.c >> +++ b/drivers/xen/grant-table.c >> @@ -45,6 +45,9 @@ >> #include <linux/workqueue.h> >> #include <linux/ratelimit.h> >> #include <linux/moduleparam.h> >> +#ifdef CONFIG_XEN_GRANT_DMA_ALLOC >> +#include <linux/dma-mapping.h> >> +#endif >> >> #include <xen/xen.h> >> #include <xen/interface/xen.h> >> @@ -57,6 +60,7 @@ >> #ifdef CONFIG_X86 >> #include <asm/xen/cpuid.h> >> #endif >> +#include <xen/mem_reservation.h> >> #include <asm/xen/hypercall.h> >> #include <asm/xen/interface.h> >> >> @@ -811,6 +815,82 @@ int gnttab_alloc_pages(int nr_pages, struct page **pages) >> } >> EXPORT_SYMBOL(gnttab_alloc_pages); >> >> +#ifdef CONFIG_XEN_GRANT_DMA_ALLOC >> +/** >> + * gnttab_dma_alloc_pages - alloc DMAable pages suitable for grant mapping into >> + * @args: arguments to the function >> + */ >> +int gnttab_dma_alloc_pages(struct gnttab_dma_alloc_args *args) >> +{ >> + unsigned long pfn, start_pfn; >> + xen_pfn_t *frames; >> + size_t size; >> + int i, ret; >> + >> + frames = kcalloc(args->nr_pages, sizeof(*frames), GFP_KERNEL); >> + if (!frames) >> + return -ENOMEM; >> + >> + size = args->nr_pages << PAGE_SHIFT; >> + if (args->coherent) >> + args->vaddr = dma_alloc_coherent(args->dev, size, >> + &args->dev_bus_addr, >> + GFP_KERNEL | __GFP_NOWARN); >> + else >> + args->vaddr = dma_alloc_wc(args->dev, size, >> + &args->dev_bus_addr, >> + GFP_KERNEL | __GFP_NOWARN); >> + if (!args->vaddr) { >> + pr_err("Failed to allocate DMA buffer of size %zu\n", size); >> + ret = -ENOMEM; >> + goto fail_free_frames; >> + } >> + >> + start_pfn = __phys_to_pfn(args->dev_bus_addr); >> + for (pfn = start_pfn, i = 0; pfn < start_pfn + args->nr_pages; >> + pfn++, i++) { >> + struct page *page = pfn_to_page(pfn); >> + >> + args->pages[i] = page; >> + frames[i] = xen_page_to_gfn(page); >> + xenmem_reservation_scrub_page(page); >> + } >> + >> + xenmem_reservation_va_mapping_reset(args->nr_pages, args->pages); >> + >> + ret = xenmem_reservation_decrease(args->nr_pages, frames); >> + if (ret != args->nr_pages) { >> + pr_err("Failed to decrease reservation for DMA buffer\n"); >> + xenmem_reservation_increase(ret, frames); >> + ret = -EFAULT; >> + goto fail_free_dma; >> + } >> + >> + ret = gnttab_pages_set_private(args->nr_pages, args->pages); >> + if (ret < 0) >> + goto fail_clear_private; >> + >> + kfree(frames); >> + return 0; >> + >> +fail_clear_private: >> + gnttab_pages_clear_private(args->nr_pages, args->pages); >> +fail_free_dma: > > Do you need to xenmem_reservation_increase()? Yes, missed that on fail_clear_private error path, will fix > >> + xenmem_reservation_va_mapping_update(args->nr_pages, args->pages, >> + frames); >> + if (args->coherent) >> + dma_free_coherent(args->dev, size, >> + args->vaddr, args->dev_bus_addr); >> + else >> + dma_free_wc(args->dev, size, >> + args->vaddr, args->dev_bus_addr); >> +fail_free_frames: >> + kfree(frames); >> + return ret; >> +} >> +EXPORT_SYMBOL(gnttab_dma_alloc_pages); >> +#endif >> + >> void gnttab_pages_clear_private(int nr_pages, struct page **pages) >> { >> int i; >> @@ -838,6 +918,50 @@ void gnttab_free_pages(int nr_pages, struct page **pages) >> } >> EXPORT_SYMBOL(gnttab_free_pages); >> >> +#ifdef CONFIG_XEN_GRANT_DMA_ALLOC >> +/** >> + * gnttab_dma_free_pages - free DMAable pages >> + * @args: arguments to the function >> + */ >> +int gnttab_dma_free_pages(struct gnttab_dma_alloc_args *args) >> +{ >> + xen_pfn_t *frames; >> + size_t size; >> + int i, ret; >> + >> + gnttab_pages_clear_private(args->nr_pages, args->pages); >> + >> + frames = kcalloc(args->nr_pages, sizeof(*frames), GFP_KERNEL); > > Any way you can do it without allocating memory? One possibility is to > keep allocated frames from gnttab_dma_alloc_pages(). (Not sure I like > that either but it's the only thing I can think of). Yes, I was also thinking about storing the allocated frames array from gnttab_dma_alloc_pages(), but that seemed not to be clear enough as the caller of the gnttab_dma_alloc_pages will need to store those frames in some context, so we can pass them on free. But the caller doesn't really need the frames which might confuse, so I decided to make those allocations on the fly. But I can still rework that to store the frames if you insist: please let me know. > > >> + if (!frames) >> + return -ENOMEM; >> + >> + for (i = 0; i < args->nr_pages; i++) >> + frames[i] = page_to_xen_pfn(args->pages[i]); > > Not xen_page_to_gfn()? Well, according to [1] it should be : /* XENMEM_populate_physmap requires a PFN based on Xen * granularity. */ frame_list[i] = page_to_xen_pfn(page);
> >> + >> + ret = xenmem_reservation_increase(args->nr_pages, frames); >> + if (ret != args->nr_pages) { >> + pr_err("Failed to decrease reservation for DMA buffer\n"); >> + ret = -EFAULT; >> + } else { >> + ret = 0; >> + } >> + >> + xenmem_reservation_va_mapping_update(args->nr_pages, args->pages, >> + frames); >> + >> + size = args->nr_pages << PAGE_SHIFT; >> + if (args->coherent) >> + dma_free_coherent(args->dev, size, >> + args->vaddr, args->dev_bus_addr); >> + else >> + dma_free_wc(args->dev, size, >> + args->vaddr, args->dev_bus_addr); >> + kfree(frames); >> + return ret; >> +} >> +EXPORT_SYMBOL(gnttab_dma_free_pages); >> +#endif >> + >> /* Handling of paged out grant targets (GNTST_eagain) */ >> #define MAX_DELAY 256 >> static inline void >> diff --git a/include/xen/grant_table.h b/include/xen/grant_table.h >> index de03f2542bb7..982e34242b9c 100644 >> --- a/include/xen/grant_table.h >> +++ b/include/xen/grant_table.h >> @@ -198,6 +198,31 @@ void gnttab_free_auto_xlat_frames(void); >> int gnttab_alloc_pages(int nr_pages, struct page **pages); >> void gnttab_free_pages(int nr_pages, struct page **pages); >> >> +#ifdef CONFIG_XEN_GRANT_DMA_ALLOC >> +struct gnttab_dma_alloc_args { >> + /* Device for which DMA memory will be/was allocated. */ >> + struct device *dev; >> + /* >> + * If set then DMA buffer is coherent and write-combine otherwise. >> + */ > Single-line comment will fix > >> + bool coherent; >> + /* >> + * Number of entries in the @pages array, defines the size >> + * of the DMA buffer. >> + */ > This can be made into single line comment as well. However, I am not > sure this comment as well as those below are necessary. Fields names are > self-describing IMO. will remove > > -boris Thank you, Oleksandr >> + int nr_pages; >> + /* Array of pages @pages filled with pages of the DMA buffer. */ >> + struct page **pages; >> + /* Virtual/CPU address of the DMA buffer. */ >> + void *vaddr; >> + /* Bus address of the DMA buffer. */ >> + dma_addr_t dev_bus_addr; >> +}; >> + >> +int gnttab_dma_alloc_pages(struct gnttab_dma_alloc_args *args); >> +int gnttab_dma_free_pages(struct gnttab_dma_alloc_args *args); >> +#endif >> + >> int gnttab_pages_set_private(int nr_pages, struct page **pages); >> void gnttab_pages_clear_private(int nr_pages, struct page **pages); >> [1] https://elixir.bootlin.com/linux/v4.17-rc7/source/drivers/xen/balloon.c#L485
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