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msix: make pba size math more uniform

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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 <dongli.zhang@oracle.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
This commit is contained in:
Dongli Zhang 2018-12-17 07:34:39 +08:00 committed by Michael S. Tsirkin
parent b9731850d7
commit 17323e8b68
1 changed files with 1 additions and 1 deletions
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2
hw/pci/msix.c
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@ -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