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Wong" , Randy Dunlap , Jeff Layton , Kent Overstreet , linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, nvdimm@lists.linux.dev, linux-cxl@vger.kernel.org, linux-fsdevel@vger.kernel.org, Amir Goldstein , Jonathan Cameron , Stefan Hajnoczi , Joanne Koong , Josef Bacik , Aravind Ramesh , Ajay Joshi , John Groves Subject: [RFC V2 04/18] dev_dax_iomap: Add dax_operations for use by fs-dax on devdax Date: Thu, 3 Jul 2025 13:50:18 -0500 Message-Id: <20250703185032.46568-5-john@groves.net> X-Mailer: git-send-email 2.39.5 (Apple Git-154) In-Reply-To: <20250703185032.46568-1-john@groves.net> References: <20250703185032.46568-1-john@groves.net> Precedence: bulk X-Mailing-List: nvdimm@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Notes about this commit: * These methods are based on pmem_dax_ops from drivers/nvdimm/pmem.c * dev_dax_direct_access() is returns the hpa, pfn and kva. The kva was newly stored as dev_dax->virt_addr by dev_dax_probe(). * The hpa/pfn are used for mmap (dax_iomap_fault()), and the kva is used for read/write (dax_iomap_rw()) * dev_dax_recovery_write() and dev_dax_zero_page_range() have not been tested yet. I'm looking for suggestions as to how to test those. Signed-off-by: John Groves --- drivers/dax/bus.c | 120 ++++++++++++++++++++++++++++++++++++++++++++-- 1 file changed, 115 insertions(+), 5 deletions(-) diff --git a/drivers/dax/bus.c b/drivers/dax/bus.c index 9d9a4ae7bbc0..61a8d1b3c07a 100644 --- a/drivers/dax/bus.c +++ b/drivers/dax/bus.c @@ -7,6 +7,10 @@ #include #include #include +#include +#include +#include +#include #include "dax-private.h" #include "bus.h" @@ -1441,6 +1445,105 @@ __weak phys_addr_t dax_pgoff_to_phys(struct dev_dax *dev_dax, pgoff_t pgoff, } EXPORT_SYMBOL_GPL(dax_pgoff_to_phys); +#if IS_ENABLED(CONFIG_DEV_DAX_IOMAP) + +static void write_dax(void *pmem_addr, struct page *page, + unsigned int off, unsigned int len) +{ + unsigned int chunk; + void *mem; + + while (len) { + mem = kmap_local_page(page); + chunk = min_t(unsigned int, len, PAGE_SIZE - off); + memcpy_flushcache(pmem_addr, mem + off, chunk); + kunmap_local(mem); + len -= chunk; + off = 0; + page++; + pmem_addr += chunk; + } +} + +static long __dev_dax_direct_access(struct dax_device *dax_dev, pgoff_t pgoff, + long nr_pages, enum dax_access_mode mode, void **kaddr, + pfn_t *pfn) +{ + struct dev_dax *dev_dax = dax_get_private(dax_dev); + size_t size = nr_pages << PAGE_SHIFT; + size_t offset = pgoff << PAGE_SHIFT; + void *virt_addr = dev_dax->virt_addr + offset; + u64 flags = PFN_DEV|PFN_MAP; + phys_addr_t phys; + pfn_t local_pfn; + size_t dax_size; + + WARN_ON(!dev_dax->virt_addr); + + if (down_read_interruptible(&dax_dev_rwsem)) + return 0; /* no valid data since we were killed */ + dax_size = dev_dax_size(dev_dax); + up_read(&dax_dev_rwsem); + + phys = dax_pgoff_to_phys(dev_dax, pgoff, nr_pages << PAGE_SHIFT); + + if (kaddr) + *kaddr = virt_addr; + + local_pfn = phys_to_pfn_t(phys, flags); /* are flags correct? */ + if (pfn) + *pfn = local_pfn; + + /* This the valid size at the specified address */ + return PHYS_PFN(min_t(size_t, size, dax_size - offset)); +} + +static int dev_dax_zero_page_range(struct dax_device *dax_dev, pgoff_t pgoff, + size_t nr_pages) +{ + long resid = nr_pages << PAGE_SHIFT; + long offset = pgoff << PAGE_SHIFT; + + /* Break into one write per dax region */ + while (resid > 0) { + void *kaddr; + pgoff_t poff = offset >> PAGE_SHIFT; + long len = __dev_dax_direct_access(dax_dev, poff, + nr_pages, DAX_ACCESS, &kaddr, NULL); + len = min_t(long, len, PAGE_SIZE); + write_dax(kaddr, ZERO_PAGE(0), offset, len); + + offset += len; + resid -= len; + } + return 0; +} + +static long dev_dax_direct_access(struct dax_device *dax_dev, + pgoff_t pgoff, long nr_pages, enum dax_access_mode mode, + void **kaddr, pfn_t *pfn) +{ + return __dev_dax_direct_access(dax_dev, pgoff, nr_pages, mode, kaddr, pfn); +} + +static size_t dev_dax_recovery_write(struct dax_device *dax_dev, pgoff_t pgoff, + void *addr, size_t bytes, struct iov_iter *i) +{ + size_t off; + + off = offset_in_page(addr); + + return _copy_from_iter_flushcache(addr, bytes, i); +} + +static const struct dax_operations dev_dax_ops = { + .direct_access = dev_dax_direct_access, + .zero_page_range = dev_dax_zero_page_range, + .recovery_write = dev_dax_recovery_write, +}; + +#endif /* IS_ENABLED(CONFIG_DEV_DAX_IOMAP) */ + static struct dev_dax *__devm_create_dev_dax(struct dev_dax_data *data) { struct dax_region *dax_region = data->dax_region; @@ -1496,11 +1599,18 @@ static struct dev_dax *__devm_create_dev_dax(struct dev_dax_data *data) } } - /* - * No dax_operations since there is no access to this device outside of - * mmap of the resulting character device. - */ - dax_dev = alloc_dax(dev_dax, NULL); + if (IS_ENABLED(CONFIG_DEV_DAX_IOMAP)) + /* holder_ops currently populated separately in a slightly + * hacky way + */ + dax_dev = alloc_dax(dev_dax, &dev_dax_ops); + else + /* + * No dax_operations since there is no access to this device + * outside of mmap of the resulting character device. + */ + dax_dev = alloc_dax(dev_dax, NULL); + if (IS_ERR(dax_dev)) { rc = PTR_ERR(dax_dev); goto err_alloc_dax; -- 2.49.0