linux-kernel - Re: [PATCH v2 4/4] KVM: add scatterlist support to xinterface

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Message-ID: <4AC878BE.9050309@redhat.com>
Date:	Sun, 04 Oct 2009 12:28:14 +0200
From:	Avi Kivity <avi@...hat.com>
To:	Gregory Haskins <ghaskins@...ell.com>
CC:	kvm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 4/4] KVM: add scatterlist support to xinterface

On 10/02/2009 10:19 PM, Gregory Haskins wrote:
> This allows a scatter-gather approach to IO, which will be useful for
> building high performance interfaces, like zero-copy and low-latency
> copy (avoiding multiple calls to copy_to/from).
>
> The interface is based on the existing scatterlist infrastructure.  The
> caller is expected to pass in a scatterlist with its "dma" field
> populated with valid GPAs.  The xinterface will then populate each
> entry by translating the GPA to a page*.
>
> The caller signifies completion by simply performing a put_page() on
> each page returned in the list.
>
> Signed-off-by: Gregory Haskins<ghaskins@...ell.com>
> ---
>
>   include/linux/kvm_xinterface.h |    4 ++
>   virt/kvm/xinterface.c          |   72 ++++++++++++++++++++++++++++++++++++++++
>   2 files changed, 76 insertions(+), 0 deletions(-)
>
> diff --git a/include/linux/kvm_xinterface.h b/include/linux/kvm_xinterface.h
> index 684b6f8..eefb575 100644
> --- a/include/linux/kvm_xinterface.h
> +++ b/include/linux/kvm_xinterface.h
> @@ -9,6 +9,7 @@
>   #include<linux/kref.h>
>   #include<linux/module.h>
>   #include<linux/file.h>
> +#include<linux/scatterlist.h>
>
>   struct kvm_xinterface;
>   struct kvm_xvmap;
> @@ -36,6 +37,9 @@ struct kvm_xinterface_ops {
>   					u64 addr,
>   					unsigned long len,
>   					unsigned long flags);
> +	unsigned long (*sgmap)(struct kvm_xinterface *intf,
> +			       struct scatterlist *sgl, int nents,
> +			       unsigned long flags);
>   	void (*release)(struct kvm_xinterface *);
>   };
>
> diff --git a/virt/kvm/xinterface.c b/virt/kvm/xinterface.c
> index c356835..16729f6 100644
> --- a/virt/kvm/xinterface.c
> +++ b/virt/kvm/xinterface.c
> @@ -467,6 +467,77 @@ fail:
>
>   }
>
> +static unsigned long
> +xinterface_sgmap(struct kvm_xinterface *intf,
> +		 struct scatterlist *sgl, int nents,
> +		 unsigned long flags)
> +{
> +	struct _xinterface     *_intf   = to_intf(intf);
> +	struct task_struct     *p       = _intf->task;
> +	struct mm_struct       *mm      = _intf->mm;
> +	struct kvm             *kvm     = _intf->kvm;
> +	struct kvm_memory_slot *memslot = NULL;
> +	bool                    kthread = !current->mm;
> +	int                     ret;
> +	struct scatterlist     *sg;
> +	int                     i;
> +
> +	down_read(&kvm->slots_lock);
> +
> +	if (kthread)
> +		use_mm(_intf->mm);
> +
> +	for_each_sg(sgl, sg, nents, i) {
> +		unsigned long           gpa    = sg_dma_address(sg);
> +		unsigned long           len    = sg_dma_len(sg);
> +		unsigned long           gfn    = gpa>>  PAGE_SHIFT;
> +		off_t                   offset = offset_in_page(gpa);
> +		unsigned long           hva;
> +		struct page            *pg;
> +
> +		/* ensure that we do not have more than one page per entry */
> +		if ((PAGE_ALIGN(len + offset)>>  PAGE_SHIFT) != 1) {
> +			ret = -EINVAL;
> +			break;
> +		}
> +
> +		/* check for a memslot-cache miss */
> +		if (!memslot
> +		    || gfn<  memslot->base_gfn
> +		    || gfn>= memslot->base_gfn + memslot->npages) {
> +			memslot = gfn_to_memslot(kvm, gfn);
> +			if (!memslot) {
> +				ret = -EFAULT;
> +				break;
> +			}
> +		}
> +
> +		hva = (memslot->userspace_addr +
> +		       (gfn - memslot->base_gfn) * PAGE_SIZE);
> +
> +		if (kthread || current->mm == mm)
> +			ret = get_user_pages_fast(hva, 1, 1,&pg);
> +		else
> +			ret = get_user_pages(p, mm, hva, 1, 1, 0,&pg, NULL);
>    

One of these needs the mm semaphore.

> +
> +		if (ret != 1) {
> +			if (ret>= 0)
> +				ret = -EFAULT;
> +			break;
> +		}
> +
> +		sg_set_page(sg, pg, len, offset);
> +		ret = 0;
> +	}
> +
> +	if (kthread)
> +		unuse_mm(_intf->mm);
> +
> +	up_read(&kvm->slots_lock);
> +
> +	return ret;
> +}
> +
>   static void
>   xinterface_release(struct kvm_xinterface *intf)
>   {
> @@ -483,6 +554,7 @@ struct kvm_xinterface_ops _xinterface_ops = {
>   	.copy_from   = xinterface_copy_from,
>   	.vmap        = xinterface_vmap,
>   	.ioevent     = xinterface_ioevent,
> +	.sgmap       = xinterface_sgmap,
>   	.release     = xinterface_release,
>   };
>
>
> --
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>    


-- 
error compiling committee.c: too many arguments to function

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