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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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