diff options
| author | Michael Brown <mcb30@ipxe.org> | 2015-06-23 20:37:55 +0100 |
|---|---|---|
| committer | Michael Brown <mcb30@ipxe.org> | 2015-06-23 20:51:19 +0100 |
| commit | e46154fbb4cbbf8ec5d93b0d81915b220fd4c7a3 (patch) | |
| tree | f03ca73408e1ae3cc98101c6ca98edff698598c6 | |
| parent | be3517c4ab4af8de973014e7e371a1c54dce8abf (diff) | |
| download | ipxe-e46154fbb4cbbf8ec5d93b0d81915b220fd4c7a3.tar.gz | |
[pci] Use flat real mode to call INT 1a,b101
Some HP BIOSes (observed with an HP ProLiant m710p Server Cartridge)
have a bug in the implementation of INT 1a,b101: they blithely assume
that real-mode code is able to read from anywhere in the 32-bit memory
space.
This problem affects the call to INT 1a,b101 made from within
pcibios_num_bus() (which uses REAL_CODE() and hence executes in
genuine real mode) but does not affect the call made from within
romprefix.S (since with a PMM BIOS, that call executes in flat real
mode anyway).
Work around the problem by explicitly calling flatten_real_mode()
before invoking INT 1a,b101. This is a rarely-used code path, and so
the extra overhead of emulating instructions in some VM configurations
(see commit 6d4deee ("[librm] Use genuine real mode to accelerate
operation in virtual machines") for more details) is negligible.
Reported-by: Wissam Shoukair <wissams@mellanox.com>
Debugged-by: Wissam Shoukair <wissams@mellanox.com>
Debugged-by: Michael Brown <mcb30@ipxe.org>
Signed-off-by: Michael Brown <mcb30@ipxe.org>
| -rw-r--r-- | src/arch/i386/interface/pcbios/pcibios.c | 6 |
1 files changed, 5 insertions, 1 deletions
diff --git a/src/arch/i386/interface/pcbios/pcibios.c b/src/arch/i386/interface/pcbios/pcibios.c index bec70bf3..34efa0b3 100644 --- a/src/arch/i386/interface/pcbios/pcibios.c +++ b/src/arch/i386/interface/pcbios/pcibios.c @@ -42,7 +42,11 @@ static int pcibios_num_bus ( void ) { int discard_a, discard_D; uint8_t max_bus; - __asm__ __volatile__ ( REAL_CODE ( "stc\n\t" + /* We issue this call using flat real mode, to work around a + * bug in some HP BIOSes. + */ + __asm__ __volatile__ ( REAL_CODE ( "call flatten_real_mode\n\t" + "stc\n\t" "int $0x1a\n\t" "jnc 1f\n\t" "xorw %%cx, %%cx\n\t" |