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Message-ID: <20091003200519.GB6601@amt.cnet>
Date: Sat, 3 Oct 2009 17:05:19 -0300
From: Marcelo Tosatti <mtosatti@...hat.com>
To: Gregory Haskins <ghaskins@...ell.com>
Cc: kvm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 2/4] KVM: introduce "xinterface" API for external
interaction with guests
On Fri, Oct 02, 2009 at 04:19:27PM -0400, Gregory Haskins wrote:
> What: xinterface is a mechanism that allows kernel modules external to
> the kvm.ko proper to interface with a running guest. It accomplishes
> this by creating an abstracted interface which does not expose any
> private details of the guest or its related KVM structures, and provides
> a mechanism to find and bind to this interface at run-time.
>
> Why: There are various subsystems that would like to interact with a KVM
> guest which are ideally suited to exist outside the domain of the kvm.ko
> core logic. For instance, external pci-passthrough, virtual-bus, and
> virtio-net modules are currently under development. In order for these
> modules to successfully interact with the guest, they need, at the very
> least, various interfaces for signaling IO events, pointer translation,
> and possibly memory mapping.
>
> The signaling case is covered by the recent introduction of the
> irqfd/ioeventfd mechanisms. This patch provides a mechanism to cover the
> other cases. Note that today we only expose pointer-translation related
> functions, but more could be added at a future date as needs arise.
>
> Example usage: QEMU instantiates a guest, and an external module "foo"
> that desires the ability to interface with the guest (say via
> open("/dev/foo")). QEMU may then pass the kvmfd to foo via an
> ioctl, such as: ioctl(foofd, FOO_SET_VMID, &kvmfd). Upon receipt, the
> foo module can issue kvm_xinterface_bind(kvmfd) to acquire
> the proper context. Internally, the struct kvm* and associated
> struct module* will remain pinned at least until the foo module calls
> kvm_xinterface_put().
> --- /dev/null
> +++ b/virt/kvm/xinterface.c
> @@ -0,0 +1,409 @@
> +/*
> + * KVM module interface - Allows external modules to interface with a guest
> + *
> + * Copyright 2009 Novell. All Rights Reserved.
> + *
> + * Author:
> + * Gregory Haskins <ghaskins@...ell.com>
> + *
> + * This file is free software; you can redistribute it and/or modify
> + * it under the terms of version 2 of the GNU General Public License
> + * as published by the Free Software Foundation.
> + *
> + * This program is distributed in the hope that it will be useful,
> + * but WITHOUT ANY WARRANTY; without even the implied warranty of
> + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
> + * GNU General Public License for more details.
> + *
> + * You should have received a copy of the GNU General Public License
> + * along with this program; if not, write to the Free Software Foundation,
> + * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301, USA.
> + */
> +
> +#include <linux/mm.h>
> +#include <linux/vmalloc.h>
> +#include <linux/highmem.h>
> +#include <linux/module.h>
> +#include <linux/mmu_context.h>
> +#include <linux/kvm_host.h>
> +#include <linux/kvm_xinterface.h>
> +
> +struct _xinterface {
> + struct kvm *kvm;
> + struct task_struct *task;
> + struct mm_struct *mm;
> + struct kvm_xinterface intf;
> + struct kvm_memory_slot *slotcache[NR_CPUS];
> +};
> +
> +struct _xvmap {
> + struct kvm_memory_slot *memslot;
> + unsigned long npages;
> + struct kvm_xvmap vmap;
> +};
> +
> +static struct _xinterface *
> +to_intf(struct kvm_xinterface *intf)
> +{
> + return container_of(intf, struct _xinterface, intf);
> +}
> +
> +#define _gfn_to_hva(gfn, memslot) \
> + (memslot->userspace_addr + (gfn - memslot->base_gfn) * PAGE_SIZE)
> +
> +/*
> + * gpa_to_hva() - translate a guest-physical to host-virtual using
> + * a per-cpu cache of the memslot.
> + *
> + * The gfn_to_memslot() call is relatively expensive, and the gpa access
> + * patterns exhibit a high degree of locality. Therefore, lets cache
> + * the last slot used on a per-cpu basis to optimize the lookup
> + *
> + * assumes slots_lock held for read
> + */
> +static unsigned long
> +gpa_to_hva(struct _xinterface *_intf, unsigned long gpa)
> +{
> + int cpu = get_cpu();
> + unsigned long gfn = gpa >> PAGE_SHIFT;
> + struct kvm_memory_slot *memslot = _intf->slotcache[cpu];
> + unsigned long addr = 0;
> +
> + if (!memslot
> + || gfn < memslot->base_gfn
> + || gfn >= memslot->base_gfn + memslot->npages) {
> +
> + memslot = gfn_to_memslot(_intf->kvm, gfn);
> + if (!memslot)
> + goto out;
> +
> + _intf->slotcache[cpu] = memslot;
> + }
> +
> + addr = _gfn_to_hva(gfn, memslot) + offset_in_page(gpa);
> +
> +out:
> + put_cpu();
> +
> + return addr;
Please optimize gfn_to_memslot() instead, so everybody benefits. It
shows very often on profiles.
> +
> + page_list = (struct page **) __get_free_page(GFP_KERNEL);
> + if (!page_list)
> + return NULL;
> +
> + down_write(&mm->mmap_sem);
> +
> + ret = get_user_pages(p, mm, addr, npages, 1, 0, page_list, NULL);
> + if (ret < 0)
> + goto out;
> +
> + ptr = vmap(page_list, npages, VM_MAP, PAGE_KERNEL);
> + if (ptr)
> + mm->locked_vm += npages;
Why don't you use gfn_to_page (here and elsewhere in the patch).
--
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