s390/pci: Fix s390_mmio_read/write with MIO

The s390_mmio_read/write syscalls are currently broken when running with
MIO.

The new pcistb_mio/pcstg_mio/pcilg_mio instructions are executed
similiarly to normal load/store instructions and do address translation
in the current address space. That means inside the kernel they are
aware of mappings into kernel address space while outside the kernel
they use user space mappings (usually created through mmap'ing a PCI
device file).

Now when existing user space applications use the s390_pci_mmio_write
and s390_pci_mmio_read syscalls, they pass I/O addresses that are mapped
into user space so as to be usable with the new instructions without
needing a syscall. Accessing these addresses with the old instructions
as done currently leads to a kernel panic.

Also, for such a user space mapping there may not exist an equivalent
kernel space mapping which means we can't just use the new instructions
in kernel space.

Instead of replicating user mappings in the kernel which then might
collide with other mappings, we can conceptually execute the new
instructions as if executed by the user space application using the
secondary address space. This even allows us to directly store to the
user pointer without the need for copy_to/from_user().

Cc: stable@vger.kernel.org
Fixes: 71ba41c9b1d9 ("s390/pci: provide support for MIO instructions")
Signed-off-by: Niklas Schnelle <schnelle@linux.ibm.com>
Reviewed-by: Sven Schnelle <svens@linux.ibm.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>

1 files changed, 8 insertions, 2 deletions

diff --git a/arch/s390/include/asm/pci_io.h b/arch/s390/include/asm/pci_io.h
index cd060b5dd8fd..e4dc64cc9c55 100644
--- a/arch/s390/include/asm/pci_io.h
+++ b/arch/s390/include/asm/pci_io.h
@@ -8,6 +8,10 @@
 #include <linux/slab.h>
 #include <asm/pci_insn.h>
 
+/* I/O size constraints */
+#define ZPCI_MAX_READ_SIZE	8
+#define ZPCI_MAX_WRITE_SIZE	128
+
 /* I/O Map */
 #define ZPCI_IOMAP_SHIFT		48
 #define ZPCI_IOMAP_ADDR_BASE		0x8000000000000000UL
@@ -140,7 +144,8 @@ static inline int zpci_memcpy_fromio(void *dst,
 
 	while (n > 0) {
 		size = zpci_get_max_write_size((u64 __force) src,
-					       (u64) dst, n, 8);
+					       (u64) dst, n,
+					       ZPCI_MAX_READ_SIZE);
 		rc = zpci_read_single(dst, src, size);
 		if (rc)
 			break;
@@ -161,7 +166,8 @@ static inline int zpci_memcpy_toio(volatile void __iomem *dst,
 
 	while (n > 0) {
 		size = zpci_get_max_write_size((u64 __force) dst,
-					       (u64) src, n, 128);
+					       (u64) src, n,
+					       ZPCI_MAX_WRITE_SIZE);
 		if (size > 8) /* main path */
 			rc = zpci_write_block(dst, src, size);
 		else