[Xen-devel] [PATCH] xen/pciback: Update data filter intersection logic.

[Andrey Grodzovsky <andrey2805@xxxxxxxxx>]

Follow up on http://www.gossamer-threads.com/lists/xen/devel/436000#436000
Using http://eli.thegreenplace.net/2008/08/15/intersection-of-1d-segments as
reference.

            New value
        |---------------|

f1                            f5
|---|                       |-----|
      f2              f4
    |-----|    f3   |-----|
            |-----|

Given a new value of the type above, Current logic will not
allow applying parts of the new value overlapping with f3 filter.
only f2 and f4.

This change allows all 3 types of overlapes to be included.
More specifically for passthrough an Industrial Ethernet Interface
(Hilscher GmbH CIFX 50E-DP(M/S)) on a HVM DomU running the
Xen 4.6 Hypervisor it allows to restore the LATENCY TIMER field
given a quirk to allow read/write for that field is already in place.
Device driver logic is such that the entire confspace  is
written in 4 byte chunks s.t. LATENCY_TIMER AND CACHE_LINE_SIZE are
arriving together in one call to xen_pcibk_config_write.

Cc: Jan Beulich <JBeulich@xxxxxxxx>
Signed-off-by: Andrey Grodzovsky <andrey2805@xxxxxxxxx>
---
 drivers/xen/xen-pciback/conf_space.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/drivers/xen/xen-pciback/conf_space.c 
b/drivers/xen/xen-pciback/conf_space.c
index 8e67336..317fb14 100644
--- a/drivers/xen/xen-pciback/conf_space.c
+++ b/drivers/xen/xen-pciback/conf_space.c
@@ -230,8 +230,7 @@ int xen_pcibk_config_write(struct pci_dev *dev, int offset, 
int size, u32 value)
                field_start = OFFSET(cfg_entry);
                field_end = OFFSET(cfg_entry) + field->size;
 
-               if ((req_start >= field_start && req_start < field_end)
-                   || (req_end > field_start && req_end <= field_end)) {
+                if (req_end >= field_start || field_end >= req_start) {
                        tmp_val = 0;
 
                        err = xen_pcibk_config_read(dev, field_start,
-- 
2.1.4


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