Re: [PATCH] IR: Fix kernel hang if interrupt remapping disable in BIOS

[Suresh Siddha <suresh.b.siddha@intel.com>]

On Wed, 2009-09-09 at 09:05 -0700, Song, Youquan wrote:
> BIOS clear DMAR table INTR_REMAP flag to disable interrupt remapping. Current
> kernel only check interrupt remapping(IR) flag in DRHD's extended capability 
> register to decide interrupt remapping support or not. But IR flag will not 
> change when BIOS disable/enable interrupt remapping. 
> 
> When user disable interrupt remapping in BIOS or BIOS often defaultly disable 
> interrupt remapping feature when BIOS is not mature.Though BIOS disable
> interrupt remapping but intr_remapping_supported function will always report 
> to OS support interrupt remapping if VT-d2 chipset populated. On this 
> cases, kernel will continue enable interrupt remapping and result kernel panic. 
> This bug exist on almost all platforms with interrupt remapping support.

I haven't encountered this before probably because bios was turning off
the interrupt-remapping support in extended capability aswell. but I do
agree that this fix is needed.

>      
> 
> This patch add DMAR table INTR_REMAP flag check before enable interrup remapping
> 
> Signed-off-by: Youquan Song <youquan.song@intel.com>

Acked-by: Suresh Siddha <suresh.b.siddha@intel.com>

David, Can you please pick this up?

thanks.

> ---
> 
> diff --git a/drivers/pci/dmar.c b/drivers/pci/dmar.c
> index a8a4383..d943e95 100644
> --- a/drivers/pci/dmar.c
> +++ b/drivers/pci/dmar.c
> @@ -1302,3 +1302,13 @@ int dmar_reenable_qi(struct intel_iommu *iommu)
>  
>  	return 0;
>  }
> +
> +/*
> + * Check interrupt remapping support in DMAR table description.
> + */
> +int dmar_ir_support(void)
> +{
> +	struct acpi_table_dmar *dmar;
> +	dmar = (struct acpi_table_dmar *)dmar_tbl;
> +	return dmar->flags & 0x1;
> +}
> diff --git a/drivers/pci/intr_remapping.c b/drivers/pci/intr_remapping.c
> index ebfa47b..ac06514 100644
> --- a/drivers/pci/intr_remapping.c
> +++ b/drivers/pci/intr_remapping.c
> @@ -611,6 +611,9 @@ int __init intr_remapping_supported(void)
>  	if (disable_intremap)
>  		return 0;
>  
> +	if (!dmar_ir_support())
> +		return 0;
> +
>  	for_each_drhd_unit(drhd) {
>  		struct intel_iommu *iommu = drhd->iommu;
>  
> diff --git a/include/linux/intel-iommu.h b/include/linux/intel-iommu.h
> index 482dc91..4f0a72a 100644
> --- a/include/linux/intel-iommu.h
> +++ b/include/linux/intel-iommu.h
> @@ -360,4 +360,6 @@ extern void qi_flush_dev_iotlb(struct intel_iommu *iommu, u16 sid, u16 qdep,
>  
>  extern int qi_submit_sync(struct qi_desc *desc, struct intel_iommu *iommu);
>  
> +extern int dmar_ir_support(void);
> +
>  #endif