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Re: [RFC 2/2] KVM: add virtio-pmem driver




> >   This patch adds virtio-pmem driver for KVM guest.
> >   Guest reads the persistent memory range information
> >   over virtio bus from Qemu and reserves the range
> >   as persistent memory. Guest also allocates a block
> >   device corresponding to the pmem range which later
> >   can be accessed with DAX compatible file systems.
> >   Idea is to use the virtio channel between guest and
> >   host to perform the block device flush for guest pmem
> >   DAX device.
> >
> >   There is work to do including DAX file system support
> >   and other advanced features.
> >
> > Signed-off-by: Pankaj Gupta <pagupta@xxxxxxxxxx>
> > ---
> >  drivers/virtio/Kconfig           |  10 ++
> >  drivers/virtio/Makefile          |   1 +
> >  drivers/virtio/virtio_pmem.c     | 322
> >  +++++++++++++++++++++++++++++++++++++++
> >  include/uapi/linux/virtio_pmem.h |  55 +++++++
> >  4 files changed, 388 insertions(+)
> >  create mode 100644 drivers/virtio/virtio_pmem.c
> >  create mode 100644 include/uapi/linux/virtio_pmem.h
> >
> > diff --git a/drivers/virtio/Kconfig b/drivers/virtio/Kconfig
> > index cff773f15b7e..0192c4bda54b 100644
> > --- a/drivers/virtio/Kconfig
> > +++ b/drivers/virtio/Kconfig
> > @@ -38,6 +38,16 @@ config VIRTIO_PCI_LEGACY
> >
> >           If unsure, say Y.
> >
> > +config VIRTIO_PMEM
> > +       tristate "Virtio pmem driver"
> > +       depends on VIRTIO
> > +       ---help---
> > +        This driver adds persistent memory range within a KVM guest.
> 
> I think we need to call this something other than persistent memory to
> make it clear that this not memory where the persistence can be
> managed from userspace. The persistence point always requires a driver
> call, so this is something distinctly different than "persistent
> memory". For example, it's a bug if this memory range ends up backing
> a device-dax range in the guest where there is no such thing as a
> driver callback to perform the flushing. How does this solution
> protect against that scenario?

yes, you are right we are not providing device_dax in this case so it should
be clear from name. Any suggestion for name?  

> 
> > +         It also associates a block device corresponding to the pmem
> > +        range.
> > +
> > +        If unsure, say M.
> > +
> >  config VIRTIO_BALLOON
> >         tristate "Virtio balloon driver"
> >         depends on VIRTIO
> > diff --git a/drivers/virtio/Makefile b/drivers/virtio/Makefile
> > index 41e30e3dc842..032ade725cc2 100644
> > --- a/drivers/virtio/Makefile
> > +++ b/drivers/virtio/Makefile
> > @@ -5,3 +5,4 @@ virtio_pci-y := virtio_pci_modern.o virtio_pci_common.o
> >  virtio_pci-$(CONFIG_VIRTIO_PCI_LEGACY) += virtio_pci_legacy.o
> >  obj-$(CONFIG_VIRTIO_BALLOON) += virtio_balloon.o
> >  obj-$(CONFIG_VIRTIO_INPUT) += virtio_input.o
> > +obj-$(CONFIG_VIRTIO_PMEM) += virtio_pmem.o
> > diff --git a/drivers/virtio/virtio_pmem.c b/drivers/virtio/virtio_pmem.c
> > new file mode 100644
> > index 000000000000..74e47cae0e24
> > --- /dev/null
> > +++ b/drivers/virtio/virtio_pmem.c
> > @@ -0,0 +1,322 @@
> > +/*
> > + * virtio-pmem driver
> > + */
> > +
> > +#include <linux/virtio.h>
> > +#include <linux/swap.h>
> > +#include <linux/workqueue.h>
> > +#include <linux/delay.h>
> > +#include <linux/slab.h>
> > +#include <linux/module.h>
> > +#include <linux/oom.h>
> > +#include <linux/wait.h>
> > +#include <linux/mm.h>
> > +#include <linux/mount.h>
> > +#include <linux/magic.h>
> > +#include <linux/virtio_pmem.h>
> > +
> > +void devm_vpmem_disable(struct device *dev, struct resource *res, void
> > *addr)
> > +{
> > +       devm_memunmap(dev, addr);
> > +       devm_release_mem_region(dev, res->start, resource_size(res));
> > +}
> > +
> > +static void pmem_flush_done(struct virtqueue *vq)
> > +{
> > +       return;
> > +};
> > +
> > +static void virtio_pmem_release_queue(void *q)
> > +{
> > +       blk_cleanup_queue(q);
> > +}
> > +
> > +static void virtio_pmem_freeze_queue(void *q)
> > +{
> > +       blk_freeze_queue_start(q);
> > +}
> > +
> > +static void virtio_pmem_release_disk(void *__pmem)
> > +{
> > +       struct virtio_pmem *pmem = __pmem;
> > +
> > +       del_gendisk(pmem->disk);
> > +       put_disk(pmem->disk);
> > +}
> 
> This code seems identical to the base pmem case, it should move to the
> shared code object.

Sure!
> 
> > +
> > +static int init_vq(struct virtio_pmem *vpmem)
> > +{
> > +       struct virtqueue *vq;
> > +
> > +       /* single vq */
> > +       vq = virtio_find_single_vq(vpmem->vdev, pmem_flush_done,
> > "flush_queue");
> > +
> > +       if (IS_ERR(vq))
> > +               return PTR_ERR(vq);
> > +
> > +       return 0;
> > +}
> > +
> > +static struct vmem_altmap *setup_pmem_pfn(struct virtio_pmem *vpmem,
> > +                       struct resource *res, struct vmem_altmap *altmap)
> > +{
> > +       u32 start_pad = 0, end_trunc = 0;
> > +       resource_size_t start, size;
> > +       unsigned long npfns;
> > +       phys_addr_t offset;
> > +
> > +       size = resource_size(res);
> > +       start = PHYS_SECTION_ALIGN_DOWN(res->start);
> > +
> > +       if (region_intersects(start, size, IORESOURCE_SYSTEM_RAM,
> > +               IORES_DESC_NONE) == REGION_MIXED) {
> > +
> > +               start = res->start;
> > +               start_pad = PHYS_SECTION_ALIGN_UP(start) - start;
> > +       }
> > +       start = res->start;
> > +       size = PHYS_SECTION_ALIGN_UP(start + size) - start;
> > +
> > +       if (region_intersects(start, size, IORESOURCE_SYSTEM_RAM,
> > +               IORES_DESC_NONE) == REGION_MIXED) {
> > +
> > +               size = resource_size(res);
> > +               end_trunc = start + size -
> > +                               PHYS_SECTION_ALIGN_DOWN(start + size);
> > +       }
> > +
> > +       start += start_pad;
> > +       size = resource_size(res);
> > +       npfns = PFN_SECTION_ALIGN_UP((size - start_pad - end_trunc - SZ_8K)
> > +                                               / PAGE_SIZE);
> > +
> > +      /*
> > +       * vmemmap_populate_hugepages() allocates the memmap array in
> > +       * HPAGE_SIZE chunks.
> > +       */
> > +       offset = ALIGN(start + SZ_8K + 64 * npfns, HPAGE_SIZE) - start;
> > +       vpmem->data_offset = offset;
> > +
> > +       struct vmem_altmap __altmap = {
> > +               .base_pfn = init_altmap_base(start+start_pad),
> > +               .reserve = init_altmap_reserve(start+start_pad),
> > +       };
> > +
> > +       res->start += start_pad;
> > +       res->end -= end_trunc;
> > +       memcpy(altmap, &__altmap, sizeof(*altmap));
> > +       altmap->free = PHYS_PFN(offset - SZ_8K);
> > +       altmap->alloc = 0;
> > +
> > +       return altmap;
> > +}
> > +
> > +static blk_status_t pmem_do_bvec(struct virtio_pmem *pmem, struct page
> > *page,
> > +                       unsigned int len, unsigned int off, bool is_write,
> > +                       sector_t sector)
> > +{
> > +       blk_status_t rc = BLK_STS_OK;
> > +       phys_addr_t pmem_off = sector * 512 + pmem->data_offset;
> > +       void *pmem_addr = pmem->virt_addr + pmem_off;
> > +
> > +       if (!is_write) {
> > +               rc = read_pmem(page, off, pmem_addr, len);
> > +                       flush_dcache_page(page);
> > +       } else {
> > +               flush_dcache_page(page);
> > +               write_pmem(pmem_addr, page, off, len);
> > +       }
> > +
> > +       return rc;
> > +}
> > +
> > +static int vpmem_rw_page(struct block_device *bdev, sector_t sector,
> > +                      struct page *page, bool is_write)
> > +{
> > +       struct virtio_pmem  *pmem = bdev->bd_queue->queuedata;
> > +       blk_status_t rc;
> > +
> > +       rc = pmem_do_bvec(pmem, page, hpage_nr_pages(page) * PAGE_SIZE,
> > +                         0, is_write, sector);
> > +
> > +       if (rc == 0)
> > +               page_endio(page, is_write, 0);
> > +
> > +       return blk_status_to_errno(rc);
> > +}
> > +
> > +#ifndef REQ_FLUSH
> > +#define REQ_FLUSH REQ_PREFLUSH
> > +#endif
> > +
> > +static blk_qc_t virtio_pmem_make_request(struct request_queue *q,
> > +                       struct bio *bio)
> > +{
> > +       blk_status_t rc = 0;
> > +       struct bio_vec bvec;
> > +       struct bvec_iter iter;
> > +       struct virtio_pmem *pmem = q->queuedata;
> > +
> > +       if (bio->bi_opf & REQ_FLUSH)
> > +               //todo host flush command
> > +
> > +       bio_for_each_segment(bvec, bio, iter) {
> > +               rc = pmem_do_bvec(pmem, bvec.bv_page, bvec.bv_len,
> > +                               bvec.bv_offset, op_is_write(bio_op(bio)),
> > +                               iter.bi_sector);
> > +               if (rc) {
> > +                       bio->bi_status = rc;
> > +                       break;
> > +               }
> > +       }
> > +
> > +       bio_endio(bio);
> > +       return BLK_QC_T_NONE;
> > +}
> 
> Again, the above could be shared by both drivers.

yes, I will do that.
> 
> > +
> > +static const struct block_device_operations pmem_fops = {
> > +       .owner =                THIS_MODULE,
> > +       .rw_page =              vpmem_rw_page,
> > +       //.revalidate_disk =    nvdimm_revalidate_disk,
> > +};
> > +
> > +static int virtio_pmem_probe(struct virtio_device *vdev)
> > +{
> > +       struct virtio_pmem *vpmem;
> > +       int err = 0;
> > +       void *addr;
> > +       struct resource *res, res_pfn;
> > +       struct request_queue *q;
> > +       struct vmem_altmap __altmap, *altmap = NULL;
> > +       struct gendisk *disk;
> > +       struct device *gendev;
> > +       int nid = dev_to_node(&vdev->dev);
> > +
> > +       if (!vdev->config->get) {
> > +               dev_err(&vdev->dev, "%s failure: config disabled\n",
> > +                       __func__);
> > +               return -EINVAL;
> > +       }
> > +
> > +       vdev->priv = vpmem = devm_kzalloc(&vdev->dev, sizeof(*vpmem),
> > +                       GFP_KERNEL);
> > +
> > +       if (!vpmem) {
> > +               err = -ENOMEM;
> > +               goto out;
> > +       }
> > +
> > +       dev_set_drvdata(&vdev->dev, vpmem);
> > +
> > +       vpmem->vdev = vdev;
> > +       err = init_vq(vpmem);
> > +       if (err)
> > +               goto out;
> > +
> > +       if (!virtio_has_feature(vdev, VIRTIO_PMEM_PLUG)) {
> > +               dev_err(&vdev->dev, "%s : pmem not supported\n",
> > +                       __func__);
> > +               goto out;
> > +       }
> > +
> > +       virtio_cread(vpmem->vdev, struct virtio_pmem_config,
> > +                       start, &vpmem->start);
> > +       virtio_cread(vpmem->vdev, struct virtio_pmem_config,
> > +                       size, &vpmem->size);
> > +
> > +       res_pfn.start = vpmem->start;
> > +       res_pfn.end   = vpmem->start + vpmem->size-1;
> > +
> > +       /* used for allocating memmap in the pmem device */
> > +       altmap        = setup_pmem_pfn(vpmem, &res_pfn, &__altmap);
> > +
> > +       res = devm_request_mem_region(&vdev->dev,
> > +                       res_pfn.start, resource_size(&res_pfn),
> > "virtio-pmem");
> > +
> > +       if (!res) {
> > +               dev_warn(&vdev->dev, "could not reserve region ");
> > +               return -EBUSY;
> > +       }
> > +
> > +       q = blk_alloc_queue_node(GFP_KERNEL, dev_to_node(&vdev->dev));
> > +
> > +       if (!q)
> > +               return -ENOMEM;
> > +
> > +       if (devm_add_action_or_reset(&vdev->dev,
> > +                               virtio_pmem_release_queue, q))
> > +               return -ENOMEM;
> > +
> > +       vpmem->pfn_flags = PFN_DEV;
> > +
> > +       /* allocate memap in pmem device itself */
> > +       if (IS_ENABLED(CONFIG_ZONE_DEVICE)) {
> > +
> > +               addr = devm_memremap_pages(&vdev->dev, res,
> > +                               &q->q_usage_counter, altmap);
> > +               vpmem->pfn_flags |= PFN_MAP;
> > +       } else
> > +               addr = devm_memremap(&vdev->dev, vpmem->start,
> > +                               vpmem->size, ARCH_MEMREMAP_PMEM);
> > +
> > +        /*
> > +         * At release time the queue must be frozen before
> > +         * devm_memremap_pages is unwound
> > +         */
> > +       if (devm_add_action_or_reset(&vdev->dev,
> > +                               virtio_pmem_freeze_queue, q))
> > +               return -ENOMEM;
> > +
> > +       if (IS_ERR(addr))
> > +               return PTR_ERR(addr);
> > +
> > +       vpmem->virt_addr = addr;
> > +       blk_queue_write_cache(q, 0, 0);
> > +       blk_queue_make_request(q, virtio_pmem_make_request);
> > +       blk_queue_physical_block_size(q, PAGE_SIZE);
> > +       blk_queue_logical_block_size(q, 512);
> > +       blk_queue_max_hw_sectors(q, UINT_MAX);
> > +       queue_flag_set_unlocked(QUEUE_FLAG_NONROT, q);
> > +       queue_flag_set_unlocked(QUEUE_FLAG_DAX, q);
> > +       q->queuedata = vpmem;
> > +
> > +       disk = alloc_disk_node(0, nid);
> > +       if (!disk)
> > +               return -ENOMEM;
> > +       vpmem->disk = disk;
> > +
> > +       disk->fops                = &pmem_fops;
> > +       disk->queue               = q;
> > +       disk->flags               = GENHD_FL_EXT_DEVT;
> > +       strcpy(disk->disk_name, "vpmem");
> > +       set_capacity(disk, vpmem->size/512);
> > +       gendev = disk_to_dev(disk);
> > +
> > +       virtio_device_ready(vdev);
> > +       device_add_disk(&vdev->dev, disk);
> > +
> > +       if (devm_add_action_or_reset(&vdev->dev,
> > +                       virtio_pmem_release_disk, vpmem))
> > +               return -ENOMEM;
> > +
> > +       revalidate_disk(disk);
> > +       return 0;
> > +out:
> > +       vdev->config->del_vqs(vdev);
> > +       return err;
> > +}
> 
> Here we have a mix of code that is common and some that is virtio
> specific, the shared code should be factored out into a common helper
> that both drivers call.

yes, i will factor this as well.
> 
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