Re: [PATCH] x86: PCI config space accessor functions should not ignore the segment argument

[Jan Beulich]

>>> On 21.07.11 at 09:10, Ingo Molnar <mingo@xxxxxxx> wrote:
>>  The access method 1 accessor, as it can be used for extended accesses
>> (on AMD systems) instead gets added checks for the passed in segment to
>> be zero (returning an error just like out of range values of the other
>> arguments would cause).
> 
> * Jan Beulich <JBeulich@xxxxxxxxxx> wrote:
> 
>> Without this change, the majority of the raw PCI config space access
>> functions silently ignore a non-zero segment argument, which is
>> certainly wrong.
>> 
>> Apart from pci_direct_conf1, all other non-MMCFG access methods get
>> used only for non-extended accesses (i.e. assigned to raw_pci_ops
>> only). Consequently, with the way raw_pci_{read,write}() work, it would
>> be a coding error to call these functions with a non-zero segment (with
>> the current call flow this cannot happen afaict).
>> 
>> 
>> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxxxx>
>> 
>> ---
>>  arch/x86/pci/ce4100.c   |    4 ++++
>>  arch/x86/pci/direct.c   |    6 ++++--
>>  arch/x86/pci/numaq_32.c |    2 ++
>>  arch/x86/pci/olpc.c     |    4 ++++
>>  arch/x86/pci/pcbios.c   |    2 ++
>>  5 files changed, 16 insertions(+), 2 deletions(-)
>> 
>> --- 3.0-rc7/arch/x86/pci/ce4100.c
>> +++ 3.0-rc7-x86-pci-access-seg/arch/x86/pci/ce4100.c
>> @@ -257,6 +257,8 @@ static int ce4100_conf_read(unsigned int
>>  {
>>  	int i;
>>  
>> +	BUG_ON(seg);
>> +
>>  	if (bus == 1) {
>>  		for (i = 0; i < ARRAY_SIZE(bus1_fixups); i++) {
>>  			if (bus1_fixups[i].dev_func == devfn &&
>> @@ -282,6 +284,8 @@ static int ce4100_conf_write(unsigned in
>>  {
>>  	int i;
>>  
>> +	BUG_ON(seg);
>> +
>>  	if (bus == 1) {
>>  		for (i = 0; i < ARRAY_SIZE(bus1_fixups); i++) {
>>  			if (bus1_fixups[i].dev_func == devfn &&
>> --- 3.0-rc7/arch/x86/pci/direct.c
>> +++ 3.0-rc7-x86-pci-access-seg/arch/x86/pci/direct.c
>> @@ -22,7 +22,7 @@ static int pci_conf1_read(unsigned int s
>>  {
>>  	unsigned long flags;
>>  
>> -	if ((bus > 255) || (devfn > 255) || (reg > 4095)) {
>> +	if (seg || (bus > 255) || (devfn > 255) || (reg > 4095)) {
>>  		*value = -1;
>>  		return -EINVAL;
>>  	}
>> @@ -53,7 +53,7 @@ static int pci_conf1_write(unsigned int
>>  {
>>  	unsigned long flags;
>>  
>> -	if ((bus > 255) || (devfn > 255) || (reg > 4095))
>> +	if (seg || (bus > 255) || (devfn > 255) || (reg > 4095))
>>  		return -EINVAL;
>>  
>>  	raw_spin_lock_irqsave(&pci_config_lock, flags);
>> @@ -97,6 +97,7 @@ static int pci_conf2_read(unsigned int s
>>  	unsigned long flags;
>>  	int dev, fn;
>>  
>> +	BUG_ON(seg);
>>  	if ((bus > 255) || (devfn > 255) || (reg > 255)) {
>>  		*value = -1;
>>  		return -EINVAL;
>> @@ -138,6 +139,7 @@ static int pci_conf2_write(unsigned int
>>  	unsigned long flags;
>>  	int dev, fn;
>>  
>> +	BUG_ON(seg);
>>  	if ((bus > 255) || (devfn > 255) || (reg > 255)) 
>>  		return -EINVAL;
>>  
>> --- 3.0-rc7/arch/x86/pci/numaq_32.c
>> +++ 3.0-rc7-x86-pci-access-seg/arch/x86/pci/numaq_32.c
>> @@ -34,6 +34,7 @@ static int pci_conf1_mq_read(unsigned in
>>  	unsigned long flags;
>>  	void *adr __iomem = XQUAD_PORT_ADDR(0xcfc, BUS2QUAD(bus));
>>  
>> +	BUG_ON(seg);
>>  	if (!value || (bus >= MAX_MP_BUSSES) || (devfn > 255) || (reg > 255))
>>  		return -EINVAL;
>>  
>> @@ -73,6 +74,7 @@ static int pci_conf1_mq_write(unsigned i
>>  	unsigned long flags;
>>  	void *adr __iomem = XQUAD_PORT_ADDR(0xcfc, BUS2QUAD(bus));
>>  
>> +	BUG_ON(seg);
>>  	if ((bus >= MAX_MP_BUSSES) || (devfn > 255) || (reg > 255)) 
>>  		return -EINVAL;
>>  
>> --- 3.0-rc7/arch/x86/pci/olpc.c
>> +++ 3.0-rc7-x86-pci-access-seg/arch/x86/pci/olpc.c
>> @@ -206,6 +206,8 @@ static int pci_olpc_read(unsigned int se
>>  {
>>  	uint32_t *addr;
>>  
>> +	BUG_ON(seg);
>> +
>>  	/* Use the hardware mechanism for non-simulated devices */
>>  	if (!is_simulated(bus, devfn))
>>  		return pci_direct_conf1.read(seg, bus, devfn, reg, len, value);
>> @@ -264,6 +266,8 @@ static int pci_olpc_read(unsigned int se
>>  static int pci_olpc_write(unsigned int seg, unsigned int bus,
>>  		unsigned int devfn, int reg, int len, uint32_t value)
>>  {
>> +	BUG_ON(seg);
>> +
>>  	/* Use the hardware mechanism for non-simulated devices */
>>  	if (!is_simulated(bus, devfn))
>>  		return pci_direct_conf1.write(seg, bus, devfn, reg, len, value);
>> --- 3.0-rc7/arch/x86/pci/pcbios.c
>> +++ 3.0-rc7-x86-pci-access-seg/arch/x86/pci/pcbios.c
>> @@ -181,6 +181,7 @@ static int pci_bios_read(unsigned int se
>>  	unsigned long flags;
>>  	unsigned long bx = (bus << 8) | devfn;
>>  
>> +	BUG_ON(seg);
>>  	if (!value || (bus > 255) || (devfn > 255) || (reg > 255))
>>  		return -EINVAL;
>>  
>> @@ -247,6 +248,7 @@ static int pci_bios_write(unsigned int s
>>  	unsigned long flags;
>>  	unsigned long bx = (bus << 8) | devfn;
>>  
>> +	BUG_ON(seg);
>>  	if ((bus > 255) || (devfn > 255) || (reg > 255)) 
>>  		return -EINVAL;
> 
> Not sure we want a BUG_ON() which crashes the box - wouldn't a 
> WARN_ON() suffice?

I can certainly convert it to a WARN_ON(), but it in fact *is* a bug if
these get called with a non-zero segment (as code path analysis says
that this is currently impossible unless the functions got called directly).
Please let me know what you prefer.

> also, the analysis/explanation is a bit incomplete:
> 
>> The access method 1 accessor, as it can be used for extended accesses
>> (on AMD systems) instead gets added checks for the passed in segment to
>> be zero (returning an error just like out of range values of the other
>> arguments would cause).
> 
> Under what circumstances can this trigger in practice, with the 
> current code?

I really don't know whether multi-segment PCI systems with AMD CPUs
are existing in practice. If they do, and if MMCFG cannot be used there
for whatever reason, accesses to segments other than zero would get
issued to the wrong device(s). I would have thought that this is what
the paragraph above says, but I certainly can add this more explicit
description...

Jan
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