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SubjectRe: [PATCH 3/8] xen/grant-table: Allow allocating buffers suitable for DMA
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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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