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SubjectRe: [PATCH 2.6.34-rcX] Do not expect PCI devices to return zeroes in PCIe space
On 05/03/10 23:21, Pan, Jacob jun wrote:
> Hi Petr,
> There are other code in the kernel makes similar assumption of accessing pci cfg above 0x100. (but they do not hang in a loop)
> e.g. in drivers/pci/probe.c
> * accesses, or the device is behind a reverse Express bridge. So we try
> * reading the dword at 0x100 which must either be 0 or a valid extended
> * capability header.
> */
> int pci_cfg_space_size_ext(struct pci_dev *dev)
> {
> u32 status;
> int pos = PCI_CFG_SPACE_SIZE;
> if (pci_read_config_dword(dev, pos,&status) != PCIBIOS_SUCCESSFUL)
> goto fail;
> if (status == 0xffffffff)
> goto fail;
> Back to the problem itself, hpa has suggested a better fix might be using cfg_size for checking in fixed_bar_cap. But we can not use it right now since we have cfg_size set to 0x100 on MRST (due to lack of PCI_CAP_ID_EXP in the PCI shim). I will negotiate with FW guys so that we have the correct return from pci_cfg_space_size() for Moorestown.
> Until then, your current fix should be good.

Thanks. Other possibility would be to modify amd_bus.c to verify that
ENABLE_CF8_EXT_CFG bit in MSR_AMD64_NB_CFG is actually writeable, and
not set PCI_HAS_IO_ECS if bit is read-as-zero. That would fix both
Moorestown code as well as pci_cfg_space_size_ext - patch below can be
applied instead of mrst.c changes.

Do not report AMD processors in VMware as ECS capable

In a VM AMD processors do not have integrated northbridge, and so their
northbridge-related MSRs do not work, and do not enable PCIe configuration
space accesses via I/O ports 0xCF8/0xCFC. Virtualized processor can be
detected by having NB_CFG register read-only.

Signed-off-by: Petr Vandrovec <>

diff --git a/arch/x86/pci/amd_bus.c b/arch/x86/pci/amd_bus.c
index fc1e8fe..cf03bff 100644
--- a/arch/x86/pci/amd_bus.c
+++ b/arch/x86/pci/amd_bus.c
@@ -349,6 +349,8 @@ static int __init early_fill_mp_bus_info(void)

#define ENABLE_CF8_EXT_CFG (1ULL << 46)

+static int ecs_ok = 1;
static void enable_pci_io_ecs(void *unused)
u64 reg;
@@ -356,6 +358,10 @@ static void enable_pci_io_ecs(void *unused)
if (!(reg & ENABLE_CF8_EXT_CFG)) {
wrmsrl(MSR_AMD64_NB_CFG, reg);
+ /* VMware implements NB_CFG MSR as read-only. Verify write worked... */
+ rdmsrl(MSR_AMD64_NB_CFG, reg);
+ if (!(reg & ENABLE_CF8_EXT_CFG))
+ ecs_ok = 0;

@@ -390,7 +396,8 @@ static int __init pci_io_ecs_init(void)
amd_cpu_notify(&amd_cpu_notifier, (unsigned long)CPU_ONLINE,
(void *)(long)cpu);
- pci_probe |= PCI_HAS_IO_ECS;
+ if (ecs_ok)
+ pci_probe |= PCI_HAS_IO_ECS;

return 0;

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