s390/pci: fix max size calculation in zpci_memcpy_toio()

The zpci_get_max_write_size() helper is used to determine the maximum
size a PCI store or load can use at a given __iomem address.

For the PCI block store the following restrictions apply:

1. The dst + len must not cross a 4K boundary in the (pseudo-)MMIO space
2. len must not exceed ZPCI_MAX_WRITE_SIZE
3. len must be a multiple of 8 bytes
4. The src address must be double word (8 byte) aligned
5. The dst address must be double word (8 byte) aligned

Otherwise only a normal PCI store which takes its src value from
a register can be used. For these PCI store restriction 1 still applies.
Similarly 1 also applies to PCI loads.

It turns out zpci_max_write_size() instead implements stricter
conditions which prevents PCI block stores from being used where they
can and should be used. In particular instead of conditions 4 and 5 it
wrongly enforces both dst and src to be size aligned. This indirectly
covers condition 1 but also prevents many legal PCI block stores.

On top of the functional shortcomings the zpci_get_max_write_size() is
misnamed as it is used for both read and write size calculations. Rename
it to zpci_get_max_io_size() and implement the listed conditions
explicitly.

Reviewed-by: Matthew Rosato <mjrosato@linux.ibm.com>
Fixes: cd24834130ac ("s390/pci: base support")
Signed-off-by: Niklas Schnelle <schnelle@linux.ibm.com>
[agordeev@linux.ibm.com replaced spaces with tabs]
Signed-off-by: Alexander Gordeev <agordeev@linux.ibm.com>

1 files changed, 6 insertions, 6 deletions

diff --git a/arch/s390/pci/pci_mmio.c b/arch/s390/pci/pci_mmio.c
index 588089332931..a90499c087f0 100644
--- a/arch/s390/pci/pci_mmio.c
+++ b/arch/s390/pci/pci_mmio.c
@@ -97,9 +97,9 @@ static inline int __memcpy_toio_inuser(void __iomem *dst,
 		return -EINVAL;
 
 	while (n > 0) {
-		size = zpci_get_max_write_size((u64 __force) dst,
-					       (u64 __force) src, n,
-					       ZPCI_MAX_WRITE_SIZE);
+		size = zpci_get_max_io_size((u64 __force) dst,
+					    (u64 __force) src, n,
+					    ZPCI_MAX_WRITE_SIZE);
 		if (size > 8) /* main path */
 			rc = __pcistb_mio_inuser(dst, src, size, &status);
 		else
@@ -242,9 +242,9 @@ static inline int __memcpy_fromio_inuser(void __user *dst,
 	u8 status;
 
 	while (n > 0) {
-		size = zpci_get_max_write_size((u64 __force) src,
-					       (u64 __force) dst, n,
-					       ZPCI_MAX_READ_SIZE);
+		size = zpci_get_max_io_size((u64 __force) src,
+					    (u64 __force) dst, n,
+					    ZPCI_MAX_READ_SIZE);
 		rc = __pcilg_mio_inuser(dst, src, size, &status);
 		if (rc)
 			break;