netfs: zero the tail of a short DIO/unbuffered readgrafted

The buffered read collector zero-fills the tail of a short read that
stops below the inode's i_size (netfs_clear_unread()), so a read that
races an extending write still returns the expected number of bytes.
The non-buffered collector path does no such thing: it just records
how much was transferred.

Add the same zero-fill for the non-buffered case, gated on
NETFS_SREQ_CLEAR_TAIL: a subreq's source sets that flag when a short
result from it is known to be safe to treat as a hole, as opposed to
NETFS_SREQ_HIT_EOF, which means the read genuinely ran off the end of
the file and should be reported short as-is. Only CLEAR_TAIL should
zero-fill here; a real EOF must stay a real short read.

No source currently sets CLEAR_TAIL on an unbuffered/DIO subrequest,
so this is inert on its own -- a following change teaches cifs to set
it in the one case that needs it.

Fixes: e2d46f2ec332 ("netfs: Change the read result collector to only use one work item")
Reviewed-by: David Howells <dhowells@redhat.com>
Reviewed-by: Namjae Jeon <linkinjeon@kernel.org>
Signed-off-by: Paulo Alcantara <pc@manguebit.org>
Cc: Christian Brauner <brauner@kernel.org>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Ronnie Sahlberg <ronniesahlberg@gmail.com>
Cc: Shyam Prasad N <sprasad@microsoft.com>
Cc: Tom Talpey <tom@talpey.com>
Cc: Bharath SM <bharathsm@microsoft.com>
Cc: stable@vger.kernel.org

1 files changed, 232 insertions, 0 deletions

diff --git a/drivers/char/adi.c b/drivers/char/adi.c
new file mode 100644
index 000000000..0849d933a
--- /dev/null
+++ b/drivers/char/adi.c
@@ -0,0 +1,232 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Privileged ADI driver for sparc64
+ *
+ * Author: Tom Hromatka <tom.hromatka@oracle.com>
+ */
+#include <linux/kernel.h>
+#include <linux/miscdevice.h>
+#include <linux/module.h>
+#include <linux/proc_fs.h>
+#include <linux/slab.h>
+#include <linux/uaccess.h>
+#include <asm/asi.h>
+
+#define MAX_BUF_SZ	PAGE_SIZE
+
+static int read_mcd_tag(unsigned long addr)
+{
+	long err;
+	int ver;
+
+	__asm__ __volatile__(
+		"1:	ldxa [%[addr]] %[asi], %[ver]\n"
+		"	mov 0, %[err]\n"
+		"2:\n"
+		"	.section .fixup,#alloc,#execinstr\n"
+		"	.align 4\n"
+		"3:	sethi %%hi(2b), %%g1\n"
+		"	jmpl  %%g1 + %%lo(2b), %%g0\n"
+		"	mov %[invalid], %[err]\n"
+		"	.previous\n"
+		"	.section __ex_table, \"a\"\n"
+		"	.align 4\n"
+		"	.word  1b, 3b\n"
+		"	.previous\n"
+		: [ver] "=r" (ver), [err] "=r" (err)
+		: [addr] "r"  (addr), [invalid] "i" (EFAULT),
+		  [asi] "i" (ASI_MCD_REAL)
+		: "memory", "g1"
+		);
+
+	if (err)
+		return -EFAULT;
+	else
+		return ver;
+}
+
+static ssize_t adi_read(struct file *file, char __user *buf,
+			size_t count, loff_t *offp)
+{
+	size_t ver_buf_sz, bytes_read = 0;
+	int ver_buf_idx = 0;
+	loff_t offset;
+	u8 *ver_buf;
+	ssize_t ret;
+
+	ver_buf_sz = min_t(size_t, count, MAX_BUF_SZ);
+	ver_buf = kmalloc(ver_buf_sz, GFP_KERNEL);
+	if (!ver_buf)
+		return -ENOMEM;
+
+	offset = (*offp) * adi_blksize();
+
+	while (bytes_read < count) {
+		ret = read_mcd_tag(offset);
+		if (ret < 0)
+			goto out;
+
+		ver_buf[ver_buf_idx] = (u8)ret;
+		ver_buf_idx++;
+		offset += adi_blksize();
+
+		if (ver_buf_idx >= ver_buf_sz) {
+			if (copy_to_user(buf + bytes_read, ver_buf,
+					 ver_buf_sz)) {
+				ret = -EFAULT;
+				goto out;
+			}
+
+			bytes_read += ver_buf_sz;
+			ver_buf_idx = 0;
+
+			ver_buf_sz = min_t(size_t, count - bytes_read,
+					   MAX_BUF_SZ);
+		}
+	}
+
+	(*offp) += bytes_read;
+	ret = bytes_read;
+out:
+	kfree(ver_buf);
+	return ret;
+}
+
+static int set_mcd_tag(unsigned long addr, u8 ver)
+{
+	long err;
+
+	__asm__ __volatile__(
+		"1:	stxa %[ver], [%[addr]] %[asi]\n"
+		"	mov 0, %[err]\n"
+		"2:\n"
+		"	.section .fixup,#alloc,#execinstr\n"
+		"	.align 4\n"
+		"3:	sethi %%hi(2b), %%g1\n"
+		"	jmpl %%g1 + %%lo(2b), %%g0\n"
+		"	mov %[invalid], %[err]\n"
+		"	.previous\n"
+		"	.section __ex_table, \"a\"\n"
+		"	.align 4\n"
+		"	.word 1b, 3b\n"
+		"	.previous\n"
+		: [err] "=r" (err)
+		: [ver] "r" (ver), [addr] "r"  (addr),
+		  [invalid] "i" (EFAULT), [asi] "i" (ASI_MCD_REAL)
+		: "memory", "g1"
+		);
+
+	if (err)
+		return -EFAULT;
+	else
+		return ver;
+}
+
+static ssize_t adi_write(struct file *file, const char __user *buf,
+			 size_t count, loff_t *offp)
+{
+	size_t ver_buf_sz, bytes_written = 0;
+	loff_t offset;
+	u8 *ver_buf;
+	ssize_t ret;
+	int i;
+
+	if (count == 0)
+		return -EINVAL;
+
+	ver_buf_sz = min_t(size_t, count, MAX_BUF_SZ);
+	ver_buf = kmalloc(ver_buf_sz, GFP_KERNEL);
+	if (!ver_buf)
+		return -ENOMEM;
+
+	offset = (*offp) * adi_blksize();
+
+	do {
+		if (copy_from_user(ver_buf, &buf[bytes_written],
+				   ver_buf_sz)) {
+			ret = -EFAULT;
+			goto out;
+		}
+
+		for (i = 0; i < ver_buf_sz; i++) {
+			ret = set_mcd_tag(offset, ver_buf[i]);
+			if (ret < 0)
+				goto out;
+
+			offset += adi_blksize();
+		}
+
+		bytes_written += ver_buf_sz;
+		ver_buf_sz = min_t(size_t, count - bytes_written, MAX_BUF_SZ);
+	} while (bytes_written < count);
+
+	(*offp) += bytes_written;
+	ret = bytes_written;
+out:
+	__asm__ __volatile__("membar #Sync");
+	kfree(ver_buf);
+	return ret;
+}
+
+static loff_t adi_llseek(struct file *file, loff_t offset, int whence)
+{
+	loff_t ret = -EINVAL;
+
+	switch (whence) {
+	case SEEK_END:
+	case SEEK_DATA:
+	case SEEK_HOLE:
+		/* unsupported */
+		return -EINVAL;
+	case SEEK_CUR:
+		if (offset == 0)
+			return file->f_pos;
+
+		offset += file->f_pos;
+		break;
+	case SEEK_SET:
+		break;
+	}
+
+	if (offset != file->f_pos) {
+		file->f_pos = offset;
+		ret = offset;
+	}
+
+	return ret;
+}
+
+static const struct file_operations adi_fops = {
+	.owner		= THIS_MODULE,
+	.llseek		= adi_llseek,
+	.read		= adi_read,
+	.write		= adi_write,
+	.fop_flags	= FOP_UNSIGNED_OFFSET,
+};
+
+static struct miscdevice adi_miscdev = {
+	.minor = MISC_DYNAMIC_MINOR,
+	.name = KBUILD_MODNAME,
+	.fops = &adi_fops,
+};
+
+static int __init adi_init(void)
+{
+	if (!adi_capable())
+		return -EPERM;
+
+	return misc_register(&adi_miscdev);
+}
+
+static void __exit adi_exit(void)
+{
+	misc_deregister(&adi_miscdev);
+}
+
+module_init(adi_init);
+module_exit(adi_exit);
+
+MODULE_AUTHOR("Tom Hromatka <tom.hromatka@oracle.com>");
+MODULE_DESCRIPTION("Privileged interface to ADI");
+MODULE_VERSION("1.0");
+MODULE_LICENSE("GPL v2");