diff mbox series

[v2,1/4] usb: early: Avoid using DbC if already enabled

Message ID d160cee9b61c0ec41c2cd5ff9b4e107011d39d8c.1620952511.git.connojdavis@gmail.com (mailing list archive)
State New
Headers show
Series [v2,1/4] usb: early: Avoid using DbC if already enabled | expand

Commit Message

Connor Davis May 14, 2021, 12:56 a.m. UTC
Check if the debug capability is enabled in early_xdbc_parse_parameter,
and if it is, return with an error. This avoids collisions with whatever
enabled the DbC prior to linux starting.

Signed-off-by: Connor Davis <connojdavis@gmail.com>
---
 drivers/usb/early/xhci-dbc.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

Comments

Jan Beulich May 17, 2021, 9:32 a.m. UTC | #1
On 14.05.2021 02:56, Connor Davis wrote:
> Check if the debug capability is enabled in early_xdbc_parse_parameter,
> and if it is, return with an error. This avoids collisions with whatever
> enabled the DbC prior to linux starting.

Doesn't this go too far and prevent use even if firmware (perhaps
mistakenly) left it enabled?

Jan

> Signed-off-by: Connor Davis <connojdavis@gmail.com>
> ---
>  drivers/usb/early/xhci-dbc.c | 10 ++++++++++
>  1 file changed, 10 insertions(+)
> 
> diff --git a/drivers/usb/early/xhci-dbc.c b/drivers/usb/early/xhci-dbc.c
> index be4ecbabdd58..ca67fddc2d36 100644
> --- a/drivers/usb/early/xhci-dbc.c
> +++ b/drivers/usb/early/xhci-dbc.c
> @@ -642,6 +642,16 @@ int __init early_xdbc_parse_parameter(char *s)
>  	}
>  	xdbc.xdbc_reg = (struct xdbc_regs __iomem *)(xdbc.xhci_base + offset);
>  
> +	if (readl(&xdbc.xdbc_reg->control) & CTRL_DBC_ENABLE) {
> +		pr_notice("xhci debug capability already in use\n");
> +		early_iounmap(xdbc.xhci_base, xdbc.xhci_length);
> +		xdbc.xdbc_reg = NULL;
> +		xdbc.xhci_base = NULL;
> +		xdbc.xhci_length = 0;
> +
> +		return -ENODEV;
> +	}
> +
>  	return 0;
>  }
>  
>
Connor Davis May 17, 2021, 1:48 p.m. UTC | #2
On 5/17/21 3:32 AM, Jan Beulich wrote:
> On 14.05.2021 02:56, Connor Davis wrote:
>> Check if the debug capability is enabled in early_xdbc_parse_parameter,
>> and if it is, return with an error. This avoids collisions with whatever
>> enabled the DbC prior to linux starting.
> Doesn't this go too far and prevent use even if firmware (perhaps
> mistakenly) left it enabled?
>
> Jan

Yes, but how is one supposed to distinguish the broken firmware and 
non-broken

firmware cases?

>
>> Signed-off-by: Connor Davis <connojdavis@gmail.com>
>> ---
>>   drivers/usb/early/xhci-dbc.c | 10 ++++++++++
>>   1 file changed, 10 insertions(+)
>>
>> diff --git a/drivers/usb/early/xhci-dbc.c b/drivers/usb/early/xhci-dbc.c
>> index be4ecbabdd58..ca67fddc2d36 100644
>> --- a/drivers/usb/early/xhci-dbc.c
>> +++ b/drivers/usb/early/xhci-dbc.c
>> @@ -642,6 +642,16 @@ int __init early_xdbc_parse_parameter(char *s)
>>   	}
>>   	xdbc.xdbc_reg = (struct xdbc_regs __iomem *)(xdbc.xhci_base + offset);
>>   
>> +	if (readl(&xdbc.xdbc_reg->control) & CTRL_DBC_ENABLE) {
>> +		pr_notice("xhci debug capability already in use\n");
>> +		early_iounmap(xdbc.xhci_base, xdbc.xhci_length);
>> +		xdbc.xdbc_reg = NULL;
>> +		xdbc.xhci_base = NULL;
>> +		xdbc.xhci_length = 0;
>> +
>> +		return -ENODEV;
>> +	}
>> +
>>   	return 0;
>>   }
>>   
>>
Thanks,

Connor
Jan Beulich May 17, 2021, 2:13 p.m. UTC | #3
On 17.05.2021 15:48, Connor Davis wrote:
> 
> On 5/17/21 3:32 AM, Jan Beulich wrote:
>> On 14.05.2021 02:56, Connor Davis wrote:
>>> Check if the debug capability is enabled in early_xdbc_parse_parameter,
>>> and if it is, return with an error. This avoids collisions with whatever
>>> enabled the DbC prior to linux starting.
>> Doesn't this go too far and prevent use even if firmware (perhaps
>> mistakenly) left it enabled?
> 
> Yes, but how is one supposed to distinguish the broken firmware and 
> non-broken
> 
> firmware cases?

Well, a first step might be to only check if running virtualized.
And then if your running virtualized, there might be a way to
inquire the hypervisor?

Jan
Connor Davis May 17, 2021, 2:24 p.m. UTC | #4
On 5/17/21 8:13 AM, Jan Beulich wrote:
> On 17.05.2021 15:48, Connor Davis wrote:
>> On 5/17/21 3:32 AM, Jan Beulich wrote:
>>> On 14.05.2021 02:56, Connor Davis wrote:
>>>> Check if the debug capability is enabled in early_xdbc_parse_parameter,
>>>> and if it is, return with an error. This avoids collisions with whatever
>>>> enabled the DbC prior to linux starting.
>>> Doesn't this go too far and prevent use even if firmware (perhaps
>>> mistakenly) left it enabled?
>> Yes, but how is one supposed to distinguish the broken firmware and
>> non-broken
>>
>> firmware cases?
> Well, a first step might be to only check if running virtualized.
> And then if your running virtualized, there might be a way to
> inquire the hypervisor?

Right, but if it was enabled by something other than a hypervisor,

or you're not running virtualized, how do you distinguish then? IMO

the proper thing to do in any case is to simply not use the DbC in linux.

Thanks,

Connor
Mathias Nyman May 18, 2021, 9:50 p.m. UTC | #5
On 17.5.2021 17.24, Connor Davis wrote:
> 
> On 5/17/21 8:13 AM, Jan Beulich wrote:
>> On 17.05.2021 15:48, Connor Davis wrote:
>>> On 5/17/21 3:32 AM, Jan Beulich wrote:
>>>> On 14.05.2021 02:56, Connor Davis wrote:
>>>>> Check if the debug capability is enabled in early_xdbc_parse_parameter,
>>>>> and if it is, return with an error. This avoids collisions with whatever
>>>>> enabled the DbC prior to linux starting.
>>>> Doesn't this go too far and prevent use even if firmware (perhaps
>>>> mistakenly) left it enabled?
>>> Yes, but how is one supposed to distinguish the broken firmware and
>>> non-broken
>>>
>>> firmware cases?
>> Well, a first step might be to only check if running virtualized.
>> And then if your running virtualized, there might be a way to
>> inquire the hypervisor?
> 
> Right, but if it was enabled by something other than a hypervisor,
> 
> or you're not running virtualized, how do you distinguish then? IMO
> 
> the proper thing to do in any case is to simply not use the DbC in linux.
> 

Sounds reasonable.

We can address "broken firmware" during the xHC handoff from BIOS to OS. 
Only first OS that loads after BIOS should see the 
"HC BIOS owned semaphore" bit set in xHCI MMIO.

If it's set then OS requests ownership, which clears BIOS owned bit.
If DbC is running here we can stop it.

-Mathias
diff mbox series

Patch

diff --git a/drivers/usb/early/xhci-dbc.c b/drivers/usb/early/xhci-dbc.c
index be4ecbabdd58..ca67fddc2d36 100644
--- a/drivers/usb/early/xhci-dbc.c
+++ b/drivers/usb/early/xhci-dbc.c
@@ -642,6 +642,16 @@  int __init early_xdbc_parse_parameter(char *s)
 	}
 	xdbc.xdbc_reg = (struct xdbc_regs __iomem *)(xdbc.xhci_base + offset);
 
+	if (readl(&xdbc.xdbc_reg->control) & CTRL_DBC_ENABLE) {
+		pr_notice("xhci debug capability already in use\n");
+		early_iounmap(xdbc.xhci_base, xdbc.xhci_length);
+		xdbc.xdbc_reg = NULL;
+		xdbc.xhci_base = NULL;
+		xdbc.xhci_length = 0;
+
+		return -ENODEV;
+	}
+
 	return 0;
 }