linux-kernel - Re: [PATCH v6 16/19] arm,arm64: do not always merge biovec if we are running on Xen

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Date:	Mon, 30 Sep 2013 12:06:46 -0400
From:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
To:	Stefano Stabellini <stefano.stabellini@...citrix.com>
Cc:	xen-devel@...ts.xensource.com, linux-kernel@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org, Ian.Campbell@...rix.com
Subject: Re: [PATCH v6 16/19] arm,arm64: do not always merge biovec if we are
 running on Xen

On Fri, Sep 27, 2013 at 05:10:04PM +0100, Stefano Stabellini wrote:
> This is similar to what it is done on X86: biovecs are prevented from merging
> otherwise every dma requests would be forced to bounce on the swiotlb buffer.
> 
> Signed-off-by: Stefano Stabellini <stefano.stabellini@...citrix.com>


This also alters the generic (well, was x86, now it is generic) code.
Perhaps that change should be made in a seperate patch and explain
what the autotranslate extra check will do for PV, PVH and HVM guests?

Wait, does that mean we had not been merging requests on HVM guests?
Is that good or bad?

> ---
>  arch/arm/include/asm/io.h   |    8 ++++++++
>  arch/arm64/include/asm/io.h |    9 +++++++++
>  drivers/xen/biomerge.c      |    4 +++-
>  3 files changed, 20 insertions(+), 1 deletions(-)
> 
> diff --git a/arch/arm/include/asm/io.h b/arch/arm/include/asm/io.h
> index d070741..c45effc 100644
> --- a/arch/arm/include/asm/io.h
> +++ b/arch/arm/include/asm/io.h
> @@ -24,9 +24,11 @@
>  #ifdef __KERNEL__
>  
>  #include <linux/types.h>
> +#include <linux/blk_types.h>
>  #include <asm/byteorder.h>
>  #include <asm/memory.h>
>  #include <asm-generic/pci_iomap.h>
> +#include <xen/xen.h>
>  
>  /*
>   * ISA I/O bus memory addresses are 1:1 with the physical address.
> @@ -372,6 +374,12 @@ extern void pci_iounmap(struct pci_dev *dev, void __iomem *addr);
>  #define BIOVEC_MERGEABLE(vec1, vec2)	\
>  	((bvec_to_phys((vec1)) + (vec1)->bv_len) == bvec_to_phys((vec2)))
>  
> +extern bool xen_biovec_phys_mergeable(const struct bio_vec *vec1,
> +				      const struct bio_vec *vec2);
> +#define BIOVEC_PHYS_MERGEABLE(vec1, vec2)				\
> +	(__BIOVEC_PHYS_MERGEABLE(vec1, vec2) &&				\
> +	 (!xen_domain() || xen_biovec_phys_mergeable(vec1, vec2)))
> +
>  #ifdef CONFIG_MMU
>  #define ARCH_HAS_VALID_PHYS_ADDR_RANGE
>  extern int valid_phys_addr_range(phys_addr_t addr, size_t size);
> diff --git a/arch/arm64/include/asm/io.h b/arch/arm64/include/asm/io.h
> index 1d12f89..c163287b 100644
> --- a/arch/arm64/include/asm/io.h
> +++ b/arch/arm64/include/asm/io.h
> @@ -22,11 +22,14 @@
>  #ifdef __KERNEL__
>  
>  #include <linux/types.h>
> +#include <linux/blk_types.h>
>  
>  #include <asm/byteorder.h>
>  #include <asm/barrier.h>
>  #include <asm/pgtable.h>
>  
> +#include <xen/xen.h>
> +
>  /*
>   * Generic IO read/write.  These perform native-endian accesses.
>   */
> @@ -263,5 +266,11 @@ extern int devmem_is_allowed(unsigned long pfn);
>   */
>  #define xlate_dev_kmem_ptr(p)	p
>  
> +extern bool xen_biovec_phys_mergeable(const struct bio_vec *vec1,
> +				      const struct bio_vec *vec2);
> +#define BIOVEC_PHYS_MERGEABLE(vec1, vec2)				\
> +	(__BIOVEC_PHYS_MERGEABLE(vec1, vec2) &&				\
> +	 (!xen_domain() || xen_biovec_phys_mergeable(vec1, vec2)))
> +
>  #endif	/* __KERNEL__ */
>  #endif	/* __ASM_IO_H */
> diff --git a/drivers/xen/biomerge.c b/drivers/xen/biomerge.c
> index 0edb91c..f323a2d 100644
> --- a/drivers/xen/biomerge.c
> +++ b/drivers/xen/biomerge.c
> @@ -2,6 +2,7 @@
>  #include <linux/io.h>
>  #include <linux/export.h>
>  #include <xen/page.h>
> +#include <xen/features.h>
>  
>  bool xen_biovec_phys_mergeable(const struct bio_vec *vec1,
>  			       const struct bio_vec *vec2)
> @@ -9,7 +10,8 @@ bool xen_biovec_phys_mergeable(const struct bio_vec *vec1,
>  	unsigned long mfn1 = pfn_to_mfn(page_to_pfn(vec1->bv_page));
>  	unsigned long mfn2 = pfn_to_mfn(page_to_pfn(vec2->bv_page));
>  
> -	return __BIOVEC_PHYS_MERGEABLE(vec1, vec2) &&
> +	return !xen_feature(XENFEAT_auto_translated_physmap) &&
> +		__BIOVEC_PHYS_MERGEABLE(vec1, vec2) &&
>  		((mfn1 == mfn2) || ((mfn1+1) == mfn2));
>  }
>  EXPORT_SYMBOL(xen_biovec_phys_mergeable);
> -- 
> 1.7.2.5
> 
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