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@xxxxxxxxxx>
---
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);
+
+ 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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