Re: [Xen-devel] [PATCH 4/4] x86/xen: use the maximum MFN to calculate the required DMA mask
On 19/11/14 17:51, Stefano Stabellini wrote:
> On Wed, 19 Nov 2014, David Vrabel wrote:
>>
>> +u64
>> +xen_swiotlb_get_required_mask(struct device *dev)
>> +{
>> +unsigned long max_mfn;
>> +
>> +max_mfn = HYPERVISOR_memory_op(XENMEM_maximum_ram_page, NULL);
>
> As Jan pointed out, I think you need to change the prototype of
> HYPERVISOR_memory_op to return long. Please do consistently across all
> relevant archs.
This doesn't help since 32-bit guests will still truncate. A new
hypercall op that returns the result in a uint64_t parameter is required.
There is another reason why max_mfn isn't suitable -- IOMMU usage so I
think we should assume a 64-bit DMA mask is required (this is actually
the change I put into XenServer's kernel).
David
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Re: [Xen-devel] [PATCH 4/4] x86/xen: use the maximum MFN to calculate the required DMA mask
>>> On 19.11.14 at 17:02, wrote: > On a Xen PV guest the DMA addresses and physical addresses are not 1:1 > (such as Xen PV guests) and the generic dma_get_required_mask() does > not return the correct mask (since it uses max_pfn). > > Some device drivers (such as mptsas, mpt2sas) use > dma_get_required_mask() to set the device's DMA mask to allow them to > use only 32-bit DMA addresses in hardware structures. This results in > unnecessary use of the SWIOTLB if DMA addresses are more than 32-bits, > impacting performance significantly. > > Provide a get_required_mask op that uses the maximum MFN to calculate > the DMA mask. > > Signed-off-by: David Vrabel Reviewed-by: Jan Beulich ___ Xen-devel mailing list Xen-devel@lists.xen.org http://lists.xen.org/xen-devel
Re: [Xen-devel] [PATCH 4/4] x86/xen: use the maximum MFN to calculate the required DMA mask
On Wed, 19 Nov 2014, David Vrabel wrote:
> On a Xen PV guest the DMA addresses and physical addresses are not 1:1
> (such as Xen PV guests) and the generic dma_get_required_mask() does
> not return the correct mask (since it uses max_pfn).
>
> Some device drivers (such as mptsas, mpt2sas) use
> dma_get_required_mask() to set the device's DMA mask to allow them to
> use only 32-bit DMA addresses in hardware structures. This results in
> unnecessary use of the SWIOTLB if DMA addresses are more than 32-bits,
> impacting performance significantly.
>
> Provide a get_required_mask op that uses the maximum MFN to calculate
> the DMA mask.
>
> Signed-off-by: David Vrabel
> ---
> arch/x86/xen/pci-swiotlb-xen.c |1 +
> drivers/xen/swiotlb-xen.c | 13 +
> include/xen/swiotlb-xen.h |4
> 3 files changed, 18 insertions(+)
>
> diff --git a/arch/x86/xen/pci-swiotlb-xen.c b/arch/x86/xen/pci-swiotlb-xen.c
> index 0e98e5d..a5d180a 100644
> --- a/arch/x86/xen/pci-swiotlb-xen.c
> +++ b/arch/x86/xen/pci-swiotlb-xen.c
> @@ -31,6 +31,7 @@ static struct dma_map_ops xen_swiotlb_dma_ops = {
> .map_page = xen_swiotlb_map_page,
> .unmap_page = xen_swiotlb_unmap_page,
> .dma_supported = xen_swiotlb_dma_supported,
> + .get_required_mask = xen_swiotlb_get_required_mask,
> };
>
> /*
> diff --git a/drivers/xen/swiotlb-xen.c b/drivers/xen/swiotlb-xen.c
> index ebd8f21..654587d 100644
> --- a/drivers/xen/swiotlb-xen.c
> +++ b/drivers/xen/swiotlb-xen.c
> @@ -42,9 +42,11 @@
> #include
> #include
> #include
> +#include
>
> #include
> #include
> +#include
>
> #include
> /*
> @@ -683,3 +685,14 @@ xen_swiotlb_set_dma_mask(struct device *dev, u64
> dma_mask)
> return 0;
> }
> EXPORT_SYMBOL_GPL(xen_swiotlb_set_dma_mask);
> +
> +u64
> +xen_swiotlb_get_required_mask(struct device *dev)
> +{
> + unsigned long max_mfn;
> +
> + max_mfn = HYPERVISOR_memory_op(XENMEM_maximum_ram_page, NULL);
As Jan pointed out, I think you need to change the prototype of
HYPERVISOR_memory_op to return long. Please do consistently across all
relevant archs.
> + return DMA_BIT_MASK(fls_long(max_mfn - 1) + PAGE_SHIFT);
> +}
> +EXPORT_SYMBOL_GPL(xen_swiotlb_get_required_mask);
> diff --git a/include/xen/swiotlb-xen.h b/include/xen/swiotlb-xen.h
> index 8b2eb93..640 100644
> --- a/include/xen/swiotlb-xen.h
> +++ b/include/xen/swiotlb-xen.h
> @@ -58,4 +58,8 @@ xen_swiotlb_dma_supported(struct device *hwdev, u64 mask);
>
> extern int
> xen_swiotlb_set_dma_mask(struct device *dev, u64 dma_mask);
> +
> +extern u64
> +xen_swiotlb_get_required_mask(struct device *dev);
> +
> #endif /* __LINUX_SWIOTLB_XEN_H */
> --
> 1.7.10.4
>
>
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[Xen-devel] [PATCH 4/4] x86/xen: use the maximum MFN to calculate the required DMA mask
On a Xen PV guest the DMA addresses and physical addresses are not 1:1
(such as Xen PV guests) and the generic dma_get_required_mask() does
not return the correct mask (since it uses max_pfn).
Some device drivers (such as mptsas, mpt2sas) use
dma_get_required_mask() to set the device's DMA mask to allow them to
use only 32-bit DMA addresses in hardware structures. This results in
unnecessary use of the SWIOTLB if DMA addresses are more than 32-bits,
impacting performance significantly.
Provide a get_required_mask op that uses the maximum MFN to calculate
the DMA mask.
Signed-off-by: David Vrabel
---
arch/x86/xen/pci-swiotlb-xen.c |1 +
drivers/xen/swiotlb-xen.c | 13 +
include/xen/swiotlb-xen.h |4
3 files changed, 18 insertions(+)
diff --git a/arch/x86/xen/pci-swiotlb-xen.c b/arch/x86/xen/pci-swiotlb-xen.c
index 0e98e5d..a5d180a 100644
--- a/arch/x86/xen/pci-swiotlb-xen.c
+++ b/arch/x86/xen/pci-swiotlb-xen.c
@@ -31,6 +31,7 @@ static struct dma_map_ops xen_swiotlb_dma_ops = {
.map_page = xen_swiotlb_map_page,
.unmap_page = xen_swiotlb_unmap_page,
.dma_supported = xen_swiotlb_dma_supported,
+ .get_required_mask = xen_swiotlb_get_required_mask,
};
/*
diff --git a/drivers/xen/swiotlb-xen.c b/drivers/xen/swiotlb-xen.c
index ebd8f21..654587d 100644
--- a/drivers/xen/swiotlb-xen.c
+++ b/drivers/xen/swiotlb-xen.c
@@ -42,9 +42,11 @@
#include
#include
#include
+#include
#include
#include
+#include
#include
/*
@@ -683,3 +685,14 @@ xen_swiotlb_set_dma_mask(struct device *dev, u64 dma_mask)
return 0;
}
EXPORT_SYMBOL_GPL(xen_swiotlb_set_dma_mask);
+
+u64
+xen_swiotlb_get_required_mask(struct device *dev)
+{
+ unsigned long max_mfn;
+
+ max_mfn = HYPERVISOR_memory_op(XENMEM_maximum_ram_page, NULL);
+
+ return DMA_BIT_MASK(fls_long(max_mfn - 1) + PAGE_SHIFT);
+}
+EXPORT_SYMBOL_GPL(xen_swiotlb_get_required_mask);
diff --git a/include/xen/swiotlb-xen.h b/include/xen/swiotlb-xen.h
index 8b2eb93..640 100644
--- a/include/xen/swiotlb-xen.h
+++ b/include/xen/swiotlb-xen.h
@@ -58,4 +58,8 @@ xen_swiotlb_dma_supported(struct device *hwdev, u64 mask);
extern int
xen_swiotlb_set_dma_mask(struct device *dev, u64 dma_mask);
+
+extern u64
+xen_swiotlb_get_required_mask(struct device *dev);
+
#endif /* __LINUX_SWIOTLB_XEN_H */
--
1.7.10.4
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