patches: Add two patches with DAX fixes

Signed-off-by: Asahi Lina <[email protected]>

patches/0019-dax-Allow-block-size-PAGE_SIZE.patch

@@ -0,0 +1,39 @@
+From ce899b86d685b28016cc27c505d1fdca468c9b2e Mon Sep 17 00:00:00 2001
+From: Asahi Lina <[email protected]>
+Date: Sun, 20 Oct 2024 01:23:41 +0900
+Subject: [PATCH 1/2] dax: Allow block size > PAGE_SIZE
+
+For virtio-dax, the file/FS blocksize is irrelevant. FUSE always uses
+large DAX blocks (2MiB), which will work with all host page sizes. Since
+we are mapping files into the DAX window on the host, the underlying
+block size of the filesystem and its block device (if any) are
+meaningless.
+
+For real devices with DAX, the only requirement should be that the FS
+block size is *at least* as large as PAGE_SIZE, to ensure that at least
+whole pages can be mapped out of the device contiguously.
+
+Fixes warning when using virtio-dax on a 4K guest with a 16K host,
+backed by tmpfs (which sets blksz == PAGE_SIZE on the host).
+
+Signed-off-by: Asahi Lina <[email protected]>
+---
+ fs/dax.c | 2 +-
+ 1 file changed, 1 insertion(+), 1 deletion(-)
+
+diff --git a/fs/dax.c b/fs/dax.c
+index becb4a6920c6..2ef3b50e8d7a 100644
+--- a/fs/dax.c
++++ b/fs/dax.c
+@@ -1032,7 +1032,7 @@ int dax_writeback_mapping_range(struct address_space *mapping,
+ 	int ret = 0;
+ 	unsigned int scanned = 0;
+
+-	if (WARN_ON_ONCE(inode->i_blkbits != PAGE_SHIFT))
++	if (WARN_ON_ONCE(inode->i_blkbits < PAGE_SHIFT))
+ 		return -EIO;
+
+ 	if (mapping_empty(mapping) || wbc->sync_mode != WB_SYNC_ALL)
+-- 
+2.47.0
+

patches/0020-mm-Fix-__wp_page_copy_user-fallback-path-for-remote-.patch

@@ -0,0 +1,86 @@
+From 9b1ab7cc1eb019d9e8ce1b63954c58eb0fbecd2c Mon Sep 17 00:00:00 2001
+From: Asahi Lina <[email protected]>
+Date: Mon, 21 Oct 2024 23:21:16 +0900
+Subject: [PATCH 2/2] mm: Fix __wp_page_copy_user fallback path for remote mm
+
+If the source page is a PFN mapping, we copy back from userspace.
+However, if this fault is a remote access, we cannot use
+__copy_from_user_inatomic. Instead, use access_remote_vm() in this case.
+
+Fixes WARN when writing to CoW mappings into a remote process, such as
+when using gdb on a binary present on a DAX filesystem.
+
+[  143.683782] ------------[ cut here ]------------
+[  143.683784] WARNING: CPU: 1 PID: 350 at mm/memory.c:2904 __wp_page_copy_user+0x120/0x2bc
+[  143.683793] CPU: 1 PID: 350 Comm: gdb Not tainted 6.6.52 #1
+[  143.683794] Hardware name: linux,dummy-virt (DT)
+[  143.683795] pstate: 61400005 (nZCv daif +PAN -UAO -TCO +DIT -SSBS BTYPE=--)
+[  143.683796] pc : __wp_page_copy_user+0x120/0x2bc
+[  143.683798] lr : __wp_page_copy_user+0x254/0x2bc
+[  143.683799] sp : ffff80008272b8b0
+[  143.683799] x29: ffff80008272b8b0 x28: 0000000000000000 x27: ffff000083bad580
+[  143.683801] x26: 0000000000000000 x25: 0000fffff7fd5000 x24: ffff000081db04c0
+[  143.683802] x23: ffff00014f24b000 x22: fffffc00053c92c0 x21: ffff000083502150
+[  143.683803] x20: 0000fffff7fd5000 x19: ffff80008272b9d0 x18: 0000000000000000
+[  143.683804] x17: ffff000081db0500 x16: ffff800080fe52a0 x15: 0000fffff7fd5000
+[  143.683804] x14: 0000000000bb1845 x13: 0000000000000080 x12: ffff80008272b880
+[  143.683805] x11: ffff000081d13600 x10: ffff000081d13608 x9 : ffff000081d1360c
+[  143.683806] x8 : ffff000083a16f00 x7 : 0000000000000010 x6 : ffff00014f24b000
+[  143.683807] x5 : ffff00014f24c000 x4 : 0000000000000000 x3 : ffff000083582000
+[  143.683807] x2 : 0000000000000f80 x1 : 0000fffff7fd5000 x0 : 0000000000001000
+[  143.683808] Call trace:
+[  143.683809]  __wp_page_copy_user+0x120/0x2bc
+[  143.683810]  wp_page_copy+0x98/0x5c0
+[  143.683813]  do_wp_page+0x250/0x530
+[  143.683814]  __handle_mm_fault+0x278/0x284
+[  143.683817]  handle_mm_fault+0x64/0x1e8
+[  143.683819]  faultin_page+0x5c/0x110
+[  143.683820]  __get_user_pages+0xc8/0x2f4
+[  143.683821]  get_user_pages_remote+0xac/0x30c
+[  143.683823]  __access_remote_vm+0xb4/0x368
+[  143.683824]  access_remote_vm+0x10/0x1c
+[  143.683826]  mem_rw.isra.0+0xc4/0x218
+[  143.683831]  mem_write+0x18/0x24
+[  143.683831]  vfs_write+0xa0/0x37c
+[  143.683834]  ksys_pwrite64+0x7c/0xc0
+[  143.683834]  __arm64_sys_pwrite64+0x20/0x2c
+[  143.683835]  invoke_syscall+0x48/0x10c
+[  143.683837]  el0_svc_common.constprop.0+0x40/0xe0
+[  143.683839]  do_el0_svc+0x1c/0x28
+[  143.683841]  el0_svc+0x3c/0xdc
+[  143.683846]  el0t_64_sync_handler+0x120/0x12c
+[  143.683848]  el0t_64_sync+0x194/0x198
+[  143.683849] ---[ end trace 0000000000000000 ]---
+
+Signed-off-by: Asahi Lina <[email protected]>
+---
+ mm/memory.c | 7 ++++++-
+ 1 file changed, 6 insertions(+), 1 deletion(-)
+
+diff --git a/mm/memory.c b/mm/memory.c
+index ebfc9768f801..277079edd24b 100644
+--- a/mm/memory.c
++++ b/mm/memory.c
+@@ -3078,13 +3078,18 @@ static inline int __wp_page_copy_user(struct page *dst, struct page *src,
+ 			update_mmu_cache_range(vmf, vma, addr, vmf->pte, 1);
+ 	}
+
++	/* If the mm is a remote mm, copy in the page using access_remote_vm() */
++	if (current->mm != mm) {
++		if (access_remote_vm(mm, (unsigned long)uaddr, kaddr, PAGE_SIZE, 0) != PAGE_SIZE)
++			goto warn;
++	}
+ 	/*
+ 	 * This really shouldn't fail, because the page is there
+ 	 * in the page tables. But it might just be unreadable,
+ 	 * in which case we just give up and fill the result with
+ 	 * zeroes.
+ 	 */
+-	if (__copy_from_user_inatomic(kaddr, uaddr, PAGE_SIZE)) {
++	else if (__copy_from_user_inatomic(kaddr, uaddr, PAGE_SIZE)) {
+ 		if (vmf->pte)
+ 			goto warn;
+
+-- 
+2.47.0
+