From: Anthony Liguori <anthony@codemonkey.ws>
To: Marcelo Tosatti <mtosatti@redhat.com>
Cc: "Michael S. Tsirkin" <mst@redhat.com>,
quintela@redhat.com, qemu-devel@nongnu.org,
Paul Brook <paul@codesourcery.com>,
amit.shah@redhat.com, kraxel@redhat.com
Subject: Re: [Qemu-devel] Re: [PATCHv2 10/12] tap: add vhost/vhostfd options
Date: Tue, 02 Mar 2010 12:13:58 -0600 [thread overview]
Message-ID: <4B8D5566.6030308@codemonkey.ws> (raw)
In-Reply-To: <20100302180025.GA27792@amt.cnet>
On 03/02/2010 12:00 PM, Marcelo Tosatti wrote:
>> - it always returns a transient mapping
>> - it may (transparently) bounce
>> - it may fail to bounce, caller must deal
>>
>> The new function I'm proposing has the following semantics:
>>
> What exactly are the purposes of the new function?
>
We need an API that can be used to obtain a persistent mapping of a
given guest physical address. We don't have that today. We can
potentially change cpu_physical_memory_map() to also accommodate this
use case but that's a second step.
>> - it always returns a persistent mapping
>>
> For hotplug? What exactly you mean persistent?
>
Hotplug cannot happen as long as a persistent mapping exists for an
address within that region. This is okay. You cannot have an active
device driver DMA'ing to a DIMM and then hot unplug it. The guest is
responsible for making sure this doesn't happen.
>> - it never bounces
>> - it will only fail if the mapping isn't ram
>>
>> A caller can use the new function to implement an optimization to
>> force the device to only work with real ram.
>>
> To bypass the address translation in exec.c?
>
No, the ultimate goal is to convert virtio ring accesses from:
static inline uint32_t vring_desc_len(target_phys_addr_t desc_pa, int i)
{
target_phys_addr_t pa;
pa = desc_pa + sizeof(VRingDesc) * i + offsetof(VRingDesc, len);
return ldl_phys(pa);
}
len = vring_desc_len(vring.desc_pa, i)
To:
len = ldl_w(vring->desc[i].len);
When host == arch, ldl_w is a nop. Otherwise, it's just a byte swap.
ldl_phys() today turns into cpu_physical_memory_read() which is very slow.
To support this, we must enforce that when a guest passes us a physical
address, we can safely obtain a persistent mapping to it. This is true
for any ram address. It's not true for MMIO memory. We have no way to
do this with cpu_physical_memory_map().
>> IOW, this is something we can use in virtio, but very little else.
>> cpu_physical_memory_map can be used in more circumstances.
>>
> Does not make much sense to me. The qdev<-> memory map mapping seems
> more important. Following your security enhancement drive, you can for
> example check whether the region can actually be mapped by the device
> and deny otherwise, or do whatever host-side memory protection tricks
> you'd like.
>
It's two independent things. Part of what makes virtio so complicated
to convert to proper bus accessors is it's use of
ldl_phys/stl_phys/etc. No other device use those functions. If we
reduce virtio to just use a map() function, it simplifies the bus
accessor conversion.
> And "cpu_ram_map" seems like the memory is accessed through cpu context,
> while it is really always device context.
>
Yes, but that's a separate effort. In fact, see
http://wiki.qemu.org/Features/RamAPI vs.
http://wiki.qemu.org/Features/PCIMemoryAPI
Regards,
Anthony Liguori
next prev parent reply other threads:[~2010-03-02 18:14 UTC|newest]
Thread overview: 70+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-02-25 18:27 [Qemu-devel] [PATCHv2 00/12] vhost-net: upstream integration Michael S. Tsirkin
2010-02-25 18:27 ` [Qemu-devel] [PATCHv2 05/12] virtio: add APIs for queue fields Michael S. Tsirkin
2010-02-25 18:49 ` Blue Swirl
2010-02-26 14:53 ` Michael S. Tsirkin
2010-02-25 19:25 ` [Qemu-devel] " Anthony Liguori
2010-02-26 8:46 ` Gleb Natapov
2010-02-25 18:28 ` [Qemu-devel] [PATCHv2 09/12] vhost: vhost net support Michael S. Tsirkin
2010-02-25 19:04 ` [Qemu-devel] " Juan Quintela
2010-02-26 14:32 ` Michael S. Tsirkin
2010-02-26 14:38 ` Anthony Liguori
2010-02-26 14:54 ` Michael S. Tsirkin
2010-02-25 19:44 ` Anthony Liguori
2010-02-26 14:49 ` Michael S. Tsirkin
2010-02-26 15:18 ` Anthony Liguori
2010-02-27 19:38 ` Michael S. Tsirkin
2010-02-28 1:59 ` Paul Brook
2010-02-28 10:15 ` Michael S. Tsirkin
2010-02-28 12:45 ` Paul Brook
2010-02-28 14:44 ` Michael S. Tsirkin
2010-02-28 15:23 ` Paul Brook
2010-02-28 15:37 ` Michael S. Tsirkin
2010-02-28 16:02 ` Anthony Liguori
2010-02-25 18:28 ` [Qemu-devel] [PATCHv2 02/12] kvm: add API to set ioeventfd Michael S. Tsirkin
2010-02-25 19:19 ` [Qemu-devel] " Anthony Liguori
2010-03-02 17:41 ` Michael S. Tsirkin
2010-02-25 18:28 ` [Qemu-devel] [PATCHv2 04/12] virtio: add notifier support Michael S. Tsirkin
2010-02-25 18:28 ` [Qemu-devel] [PATCHv2 01/12] tap: add interface to get device fd Michael S. Tsirkin
2010-02-25 18:28 ` [Qemu-devel] [PATCHv2 07/12] virtio: move typedef to qemu-common Michael S. Tsirkin
2010-02-25 18:28 ` [Qemu-devel] [PATCHv2 10/12] tap: add vhost/vhostfd options Michael S. Tsirkin
2010-02-25 19:47 ` [Qemu-devel] " Anthony Liguori
2010-02-26 14:51 ` Michael S. Tsirkin
2010-02-26 15:23 ` Anthony Liguori
2010-02-27 19:44 ` Michael S. Tsirkin
2010-02-28 16:08 ` Anthony Liguori
2010-02-28 17:19 ` Michael S. Tsirkin
2010-02-28 20:57 ` Anthony Liguori
2010-02-28 21:01 ` Michael S. Tsirkin
2010-02-28 22:38 ` Anthony Liguori
2010-02-28 22:39 ` Paul Brook
2010-03-01 19:27 ` Michael S. Tsirkin
2010-03-01 21:54 ` Anthony Liguori
2010-03-02 9:57 ` Michael S. Tsirkin
2010-03-02 14:07 ` Anthony Liguori
2010-03-02 14:33 ` Paul Brook
2010-03-02 14:39 ` Anthony Liguori
2010-03-02 14:55 ` Paul Brook
2010-03-02 15:33 ` Anthony Liguori
2010-03-02 15:53 ` Paul Brook
2010-03-02 15:56 ` Michael S. Tsirkin
2010-03-02 16:12 ` Anthony Liguori
2010-03-02 16:21 ` Marcelo Tosatti
2010-03-02 16:12 ` Marcelo Tosatti
2010-03-02 16:56 ` Anthony Liguori
2010-03-02 17:00 ` Michael S. Tsirkin
2010-03-02 18:00 ` Marcelo Tosatti
2010-03-02 18:13 ` Anthony Liguori [this message]
2010-03-02 22:41 ` Paul Brook
2010-03-03 14:15 ` Anthony Liguori
2010-03-03 14:43 ` Paul Brook
2010-03-03 16:24 ` Marcelo Tosatti
2010-02-25 18:28 ` [Qemu-devel] [PATCHv2 11/12] tap: add API to retrieve vhost net header Michael S. Tsirkin
2010-02-25 18:28 ` [Qemu-devel] [PATCHv2 06/12] virtio: add set_status callback Michael S. Tsirkin
2010-02-25 18:28 ` [Qemu-devel] [PATCHv2 08/12] virtio-pci: fill in notifier support Michael S. Tsirkin
2010-02-25 19:30 ` [Qemu-devel] " Anthony Liguori
2010-02-28 20:02 ` Michael S. Tsirkin
2010-02-25 18:28 ` [Qemu-devel] [PATCHv2 03/12] notifier: event notifier implementation Michael S. Tsirkin
2010-02-25 19:22 ` [Qemu-devel] " Anthony Liguori
2010-02-28 19:59 ` Michael S. Tsirkin
2010-02-25 18:28 ` [Qemu-devel] [PATCHv2 12/12] virtio-net: vhost net support Michael S. Tsirkin
2010-02-25 19:49 ` [Qemu-devel] Re: [PATCHv2 00/12] vhost-net: upstream integration Anthony Liguori
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