[PATCH resend] powernv/iommu: disable IOMMU bypass with param iommu=nobypass

[PATCH resend] powernv/iommu: disable IOMMU bypass with param iommu=nobypass

[Thadeu Lima de Souza Cascardo]

When IOMMU bypass is enabled, a PCI device can read and write memory
that was not mapped by the driver without causing an EEH. That might
cause memory corruption, for example.

When we disable bypass, DMA reads and writes to addresses not mapped by
the IOMMU will cause an EEH, allowing us to debug such issues.

Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@linux.vnet.ibm.com>
Reviewed-by: Gavin Shan <gwshan@linux.vnet.ibm.com>
---
 Documentation/kernel-parameters.txt       |    2 ++
 arch/powerpc/platforms/powernv/pci-ioda.c |   24 +++++++++++++++++++++++-
 2 files changed, 25 insertions(+), 1 deletion(-)

diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index 4df73da..7dedfe5 100644
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -1493,6 +1493,8 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
 		forcesac
 		soft
 		pt		[x86, IA-64]
+		nobypass	[PPC/POWERNV]
+			Disable IOMMU bypass, using IOMMU for PCI devices.
 
 
 	io7=		[HW] IO7 for Marvel based alpha systems
diff --git a/arch/powerpc/platforms/powernv/pci-ioda.c b/arch/powerpc/platforms/powernv/pci-ioda.c
index fac88ed..f942a19 100644
--- a/arch/powerpc/platforms/powernv/pci-ioda.c
+++ b/arch/powerpc/platforms/powernv/pci-ioda.c
@@ -75,6 +75,27 @@ static void pe_level_printk(const struct pnv_ioda_pe *pe, const char *level,
 #define pe_info(pe, fmt, ...)					\
 	pe_level_printk(pe, KERN_INFO, fmt, ##__VA_ARGS__)
 
+static bool pnv_iommu_bypass_disabled __read_mostly;
+
+static int __init iommu_setup(char *str)
+{
+	if (!str)
+		return -EINVAL;
+	while (*str) {
+		if (!strncmp(str, "nobypass", 8)) {
+			pnv_iommu_bypass_disabled = true;
+			pr_info("PowerNV: IOMMU bypass window disabled.\n");
+		}
+		str += strcspn(str, ",");
+		if (*str == ',')
+			str++;
+	}
+
+	return 0;
+}
+
+early_param("iommu", iommu_setup);
+
 /*
  * stdcix is only supposed to be used in hypervisor real mode as per
  * the architecture spec
@@ -1348,7 +1369,8 @@ static void pnv_pci_ioda2_setup_dma_pe(struct pnv_phb *phb,
 		pnv_ioda_setup_bus_dma(pe, pe->pbus, true);
 
 	/* Also create a bypass window */
-	pnv_pci_ioda2_setup_bypass_pe(phb, pe);
+	if (!pnv_iommu_bypass_disabled)
+		pnv_pci_ioda2_setup_bypass_pe(phb, pe);
 	return;
 fail:
 	if (pe->tce32_seg >= 0)
-- 
1.7.10.4

Re: [PATCH resend] powernv/iommu: disable IOMMU bypass with param iommu=nobypass

[Michael Ellerman]

On Wed, 2015-01-21 at 13:23 -0200, Thadeu Lima de Souza Cascardo wrote:
> When IOMMU bypass is enabled, a PCI device can read and write memory
> that was not mapped by the driver without causing an EEH. That might
> cause memory corruption, for example.
> 
> When we disable bypass, DMA reads and writes to addresses not mapped by
> the IOMMU will cause an EEH, allowing us to debug such issues.
> 
> Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@linux.vnet.ibm.com>
> Reviewed-by: Gavin Shan <gwshan@linux.vnet.ibm.com>
> ---
>  Documentation/kernel-parameters.txt       |    2 ++
>  arch/powerpc/platforms/powernv/pci-ioda.c |   24 +++++++++++++++++++++++-
>  2 files changed, 25 insertions(+), 1 deletion(-)

Is this unchanged since v2?

It's marked as under review in patchwork which means I'm looking at it:

  http://patchwork.ozlabs.org/patch/402682/


Please check patchwork in future.

cheers

Re: [PATCH resend] powernv/iommu: disable IOMMU bypass with param iommu=nobypass

[cascardo]

On Thu, Jan 22, 2015 at 12:05:31PM +1100, Michael Ellerman wrote:
> On Wed, 2015-01-21 at 13:23 -0200, Thadeu Lima de Souza Cascardo wrote:
> > When IOMMU bypass is enabled, a PCI device can read and write memory
> > that was not mapped by the driver without causing an EEH. That might
> > cause memory corruption, for example.
> > 
> > When we disable bypass, DMA reads and writes to addresses not mapped by
> > the IOMMU will cause an EEH, allowing us to debug such issues.
> > 
> > Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@linux.vnet.ibm.com>
> > Reviewed-by: Gavin Shan <gwshan@linux.vnet.ibm.com>
> > ---
> >  Documentation/kernel-parameters.txt       |    2 ++
> >  arch/powerpc/platforms/powernv/pci-ioda.c |   24 +++++++++++++++++++++++-
> >  2 files changed, 25 insertions(+), 1 deletion(-)
> 
> Is this unchanged since v2?
> 

Yes, it's unchanged, just rebased.

Cascardo.

> It's marked as under review in patchwork which means I'm looking at it:
> 
>   http://patchwork.ozlabs.org/patch/402682/
> 
> 
> Please check patchwork in future.
> 
> cheers
> 
> 
> _______________________________________________
> Linuxppc-dev mailing list
> Linuxppc-dev@lists.ozlabs.org
> https://lists.ozlabs.org/listinfo/linuxppc-dev

Re: [PATCH resend] powernv/iommu: disable IOMMU bypass with param iommu=nobypass

[Michael Ellerman]

On Wed, 2015-01-21 at 13:23 -0200, Thadeu Lima de Souza Cascardo wrote:
> diff --git a/arch/powerpc/platforms/powernv/pci-ioda.c b/arch/powerpc/platforms/powernv/pci-ioda.c
> index fac88ed..f942a19 100644
> --- a/arch/powerpc/platforms/powernv/pci-ioda.c
> +++ b/arch/powerpc/platforms/powernv/pci-ioda.c
> @@ -75,6 +75,27 @@ static void pe_level_printk(const struct pnv_ioda_pe *pe, const char *level,
>  #define pe_info(pe, fmt, ...)					\
>  	pe_level_printk(pe, KERN_INFO, fmt, ##__VA_ARGS__)
>  
> +static bool pnv_iommu_bypass_disabled __read_mostly;
> +
> +static int __init iommu_setup(char *str)
> +{
> +	if (!str)
> +		return -EINVAL;
> +	while (*str) {
> +		if (!strncmp(str, "nobypass", 8)) {
> +			pnv_iommu_bypass_disabled = true;
> +			pr_info("PowerNV: IOMMU bypass window disabled.\n");

I added a break here.

> +		}
> +		str += strcspn(str, ",");
> +		if (*str == ',')
> +			str++;
> +	}
> +
> +	return 0;
> +}
> +
> +early_param("iommu", iommu_setup);

cheers