[PATCH] powerpc/xive: Prevent page fault issues in the machine crash handler

[PATCH] powerpc/xive: Prevent page fault issues in the machine crash handler

[Cédric Le Goater]

When the machine crash handler is invoked, all interrupts are masked
but interrupts which have not been started yet do not have an ESB page
mapped in the Linux address space. This crashes the 'crash kexec'
sequence on sPAPR guests.

To fix, force the mapping of the ESB page when an interrupt is being
mapped in the Linux IRQ number space. This is done by setting the
initial state of the interrupt to OFF which is not necessarily the
case on PowerNV.

Signed-off-by: Cédric Le Goater <clg@kaod.org>
---
 arch/powerpc/sysdev/xive/common.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/arch/powerpc/sysdev/xive/common.c b/arch/powerpc/sysdev/xive/common.c
index df832b09e3e9..f5fadbd2533a 100644
--- a/arch/powerpc/sysdev/xive/common.c
+++ b/arch/powerpc/sysdev/xive/common.c
@@ -1035,6 +1035,15 @@ static int xive_irq_alloc_data(unsigned int virq, irq_hw_number_t hw)
 	xd->target = XIVE_INVALID_TARGET;
 	irq_set_handler_data(virq, xd);
 
+	/*
+	 * Turn OFF by default the interrupt being mapped. A side
+	 * effect of this check is the mapping the ESB page of the
+	 * interrupt in the Linux address space. This prevents page
+	 * fault issues in the crash handler which masks all
+	 * interrupts.
+	 */
+	xive_esb_read(xd, XIVE_ESB_SET_PQ_01);
+
 	return 0;
 }
 
-- 
2.21.0

Re: [PATCH] powerpc/xive: Prevent page fault issues in the machine crash handler

[Greg Kurz]

On Thu, 31 Oct 2019 07:31:00 +0100
Cédric Le Goater <clg@kaod.org> wrote:

> When the machine crash handler is invoked, all interrupts are masked
> but interrupts which have not been started yet do not have an ESB page
> mapped in the Linux address space. This crashes the 'crash kexec'
> sequence on sPAPR guests.
> 
> To fix, force the mapping of the ESB page when an interrupt is being
> mapped in the Linux IRQ number space. This is done by setting the
> initial state of the interrupt to OFF which is not necessarily the
> case on PowerNV.
> 
> Signed-off-by: Cédric Le Goater <clg@kaod.org>
> ---

Reviewed-by: Greg Kurz <groug@kaod.org>

>  arch/powerpc/sysdev/xive/common.c | 9 +++++++++
>  1 file changed, 9 insertions(+)
> 
> diff --git a/arch/powerpc/sysdev/xive/common.c b/arch/powerpc/sysdev/xive/common.c
> index df832b09e3e9..f5fadbd2533a 100644
> --- a/arch/powerpc/sysdev/xive/common.c
> +++ b/arch/powerpc/sysdev/xive/common.c
> @@ -1035,6 +1035,15 @@ static int xive_irq_alloc_data(unsigned int virq, irq_hw_number_t hw)
>  	xd->target = XIVE_INVALID_TARGET;
>  	irq_set_handler_data(virq, xd);
>  
> +	/*
> +	 * Turn OFF by default the interrupt being mapped. A side
> +	 * effect of this check is the mapping the ESB page of the
> +	 * interrupt in the Linux address space. This prevents page
> +	 * fault issues in the crash handler which masks all
> +	 * interrupts.
> +	 */
> +	xive_esb_read(xd, XIVE_ESB_SET_PQ_01);
> +
>  	return 0;
>  }
>  

Re: [PATCH] powerpc/xive: Prevent page fault issues in the machine crash handler

[Michael Ellerman]

Cédric Le Goater <clg@kaod.org> writes:
> When the machine crash handler is invoked, all interrupts are masked
> but interrupts which have not been started yet do not have an ESB page
> mapped in the Linux address space. This crashes the 'crash kexec'
> sequence on sPAPR guests.

This sounds like it needs a Fixes/stable tag?

I used these:

  Fixes: 243e25112d06 ("powerpc/xive: Native exploitation of the XIVE interrupt controller")
  Cc: stable@vger.kernel.org # v4.12+

Please tell me if you think that's wrong.

cheers


> diff --git a/arch/powerpc/sysdev/xive/common.c b/arch/powerpc/sysdev/xive/common.c
> index df832b09e3e9..f5fadbd2533a 100644
> --- a/arch/powerpc/sysdev/xive/common.c
> +++ b/arch/powerpc/sysdev/xive/common.c
> @@ -1035,6 +1035,15 @@ static int xive_irq_alloc_data(unsigned int virq, irq_hw_number_t hw)
>  	xd->target = XIVE_INVALID_TARGET;
>  	irq_set_handler_data(virq, xd);
>  
> +	/*
> +	 * Turn OFF by default the interrupt being mapped. A side
> +	 * effect of this check is the mapping the ESB page of the
> +	 * interrupt in the Linux address space. This prevents page
> +	 * fault issues in the crash handler which masks all
> +	 * interrupts.
> +	 */
> +	xive_esb_read(xd, XIVE_ESB_SET_PQ_01);
> +
>  	return 0;
>  }
>  
> -- 
> 2.21.0

Re: [PATCH] powerpc/xive: Prevent page fault issues in the machine crash handler

[Cédric Le Goater]

On 12/11/2019 13:44, Michael Ellerman wrote:
> Cédric Le Goater <clg@kaod.org> writes:
>> When the machine crash handler is invoked, all interrupts are masked
>> but interrupts which have not been started yet do not have an ESB page
>> mapped in the Linux address space. This crashes the 'crash kexec'
>> sequence on sPAPR guests.
> 
> This sounds like it needs a Fixes/stable tag?

yes.

> I used these:
> 
>   Fixes: 243e25112d06 ("powerpc/xive: Native exploitation of the XIVE interrupt controller")
>   Cc: stable@vger.kernel.org # v4.12+
>
> Please tell me if you think that's wrong.

Looks OK to me. 

Thanks,

C. 


 
> cheers
> 
> 
>> diff --git a/arch/powerpc/sysdev/xive/common.c b/arch/powerpc/sysdev/xive/common.c
>> index df832b09e3e9..f5fadbd2533a 100644
>> --- a/arch/powerpc/sysdev/xive/common.c
>> +++ b/arch/powerpc/sysdev/xive/common.c
>> @@ -1035,6 +1035,15 @@ static int xive_irq_alloc_data(unsigned int virq, irq_hw_number_t hw)
>>  	xd->target = XIVE_INVALID_TARGET;
>>  	irq_set_handler_data(virq, xd);
>>  
>> +	/*
>> +	 * Turn OFF by default the interrupt being mapped. A side
>> +	 * effect of this check is the mapping the ESB page of the
>> +	 * interrupt in the Linux address space. This prevents page
>> +	 * fault issues in the crash handler which masks all
>> +	 * interrupts.
>> +	 */
>> +	xive_esb_read(xd, XIVE_ESB_SET_PQ_01);
>> +
>>  	return 0;
>>  }
>>  
>> -- 
>> 2.21.0

Re: [PATCH] powerpc/xive: Prevent page fault issues in the machine crash handler

[Michael Ellerman]

[-- Warning: decoded text below may be mangled, UTF-8 assumed --]
[-- Attachment #1: Type: text/plain, Size: 721 bytes --]

On Thu, 2019-10-31 at 06:31:00 UTC, =?UTF-8?q?C=C3=A9dric=20Le=20Goater?= wrote:
> When the machine crash handler is invoked, all interrupts are masked
> but interrupts which have not been started yet do not have an ESB page
> mapped in the Linux address space. This crashes the 'crash kexec'
> sequence on sPAPR guests.
> 
> To fix, force the mapping of the ESB page when an interrupt is being
> mapped in the Linux IRQ number space. This is done by setting the
> initial state of the interrupt to OFF which is not necessarily the
> case on PowerNV.
> 
> Signed-off-by: Cédric Le Goater <clg@kaod.org>

Applied to powerpc next, thanks.

https://git.kernel.org/powerpc/c/1ca3dec2b2dff9d286ce6cd64108bda0e98f9710

cheers