[Qemu-devel] [PULL 02/44] msix: make pba size math more uniform

[Michael S. Tsirkin]

From: Dongli Zhang <address@hidden>

In msix_exclusive_bar the bar_pba_size is more than what the pba is
expected to have, although this never affects the bar size.

Specifically, the math in msix_init_exclusive_bar allocates too much
memory in some cases.

For example consider nentries = 8.  msix_exclusive_bar will give us
bar_pba_size = 16.  So 16 bytes.  However 8 bytes would be enough - this
is all that the spec requires.

So in practice bar_pba_size sometimes allocates an extra 8 bytes but
never more.

Since each MSIX entry size is 16 bytes, and since we make sure that
table+pba is a power of two, this always leaves a multiple of 16 bytes
for the PBA, so extra 8 bytes have no effect.

However, its ugly to have pba size temporary variable have an incorrect
value.  For consistency switch to the formula used in msix_init.

Signed-off-by: Dongli Zhang <address@hidden>
Reviewed-by: Michael S. Tsirkin <address@hidden>
Signed-off-by: Michael S. Tsirkin <address@hidden>
---
 hw/pci/msix.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/hw/pci/msix.c b/hw/pci/msix.c
index c7bdbeda9e..4e336416a7 100644
--- a/hw/pci/msix.c
+++ b/hw/pci/msix.c
@@ -345,7 +345,7 @@ int msix_init_exclusive_bar(PCIDevice *dev, unsigned short 
nentries,
     char *name;
     uint32_t bar_size = 4096;
     uint32_t bar_pba_offset = bar_size / 2;
-    uint32_t bar_pba_size = (nentries / 8 + 1) * 8;
+    uint32_t bar_pba_size = QEMU_ALIGN_UP(nentries, 64) / 8;
 
     /*
      * Migration compatibility dictates that this remains a 4k
-- 
MST