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Message-ID: <20160718055037.GA8051@danjae.aot.lge.com>
Date: Mon, 18 Jul 2016 14:50:37 +0900
From: Namhyung Kim <namhyung@...nel.org>
To: Kees Cook <keescook@...omium.org>
Cc: LKML <linux-kernel@...r.kernel.org>,
Paolo Bonzini <pbonzini@...hat.com>,
Radim Kr??m???? <rkrcmar@...hat.com>,
"Michael S. Tsirkin" <mst@...hat.com>,
Anthony Liguori <aliguori@...zon.com>,
Anton Vorontsov <anton@...msg.org>,
Colin Cross <ccross@...roid.com>,
Tony Luck <tony.luck@...el.com>,
Steven Rostedt <rostedt@...dmis.org>,
Ingo Molnar <mingo@...nel.org>,
Minchan Kim <minchan@...nel.org>, KVM <kvm@...r.kernel.org>,
qemu-devel <qemu-devel@...gnu.org>,
"virtualization@...ts.linux-foundation.org"
<virtualization@...ts.linux-foundation.org>
Subject: Re: [PATCH 1/3] virtio: Basic implementation of virtio pstore driver
Hello,
On Sun, Jul 17, 2016 at 10:12:26PM -0700, Kees Cook wrote:
> On Sun, Jul 17, 2016 at 9:37 PM, Namhyung Kim <namhyung@...nel.org> wrote:
> > The virtio pstore driver provides interface to the pstore subsystem so
> > that the guest kernel's log/dump message can be saved on the host
> > machine. Users can access the log file directly on the host, or on the
> > guest at the next boot using pstore filesystem. It currently deals with
> > kernel log (printk) buffer only, but we can extend it to have other
> > information (like ftrace dump) later.
> >
> > It supports legacy PCI device using single order-2 page buffer. As all
> > operation of pstore is synchronous, it would be fine IMHO. However I
> > don't know how to make write operation synchronous since it's called
> > with a spinlock held (from any context including NMI).
> >
> > Cc: Paolo Bonzini <pbonzini@...hat.com>
> > Cc: Radim Kr??m???? <rkrcmar@...hat.com>
> > Cc: "Michael S. Tsirkin" <mst@...hat.com>
> > Cc: Anthony Liguori <aliguori@...zon.com>
> > Cc: Anton Vorontsov <anton@...msg.org>
> > Cc: Colin Cross <ccross@...roid.com>
> > Cc: Kees Cook <keescook@...omium.org>
> > Cc: Tony Luck <tony.luck@...el.com>
> > Cc: Steven Rostedt <rostedt@...dmis.org>
> > Cc: Ingo Molnar <mingo@...nel.org>
> > Cc: Minchan Kim <minchan@...nel.org>
> > Cc: kvm@...r.kernel.org
> > Cc: qemu-devel@...gnu.org
> > Cc: virtualization@...ts.linux-foundation.org
> > Signed-off-by: Namhyung Kim <namhyung@...nel.org>
>
> This looks great to me! I'd love to use this in qemu. (Right now I go
> through hoops to use the ramoops backend for testing.)
>
> Reviewed-by: Kees Cook <keescook@...omium.org>
Thank you!
>
> Notes below...
>
[SNIP]
> > +static u16 to_virtio_type(struct virtio_pstore *vps, enum pstore_type_id type)
> > +{
> > + u16 ret;
> > +
> > + switch (type) {
> > + case PSTORE_TYPE_DMESG:
> > + ret = cpu_to_virtio16(vps->vdev, VIRTIO_PSTORE_TYPE_DMESG);
> > + break;
> > + default:
> > + ret = cpu_to_virtio16(vps->vdev, VIRTIO_PSTORE_TYPE_UNKNOWN);
> > + break;
> > + }
>
> I would love to see this support PSTORE_TYPE_CONSOLE too. It should be
> relatively easy to add: I think it'd just be another virtio command?
Do you want to append the data to the host file as guest does
printk()? I think it needs some kind of buffer management, but it's
not hard to add IMHO.
>
> > +
> > + return ret;
> > +}
> > +
[SNIP]
> > +static int notrace virt_pstore_write(enum pstore_type_id type,
> > + enum kmsg_dump_reason reason,
> > + u64 *id, unsigned int part, int count,
> > + bool compressed, size_t size,
> > + struct pstore_info *psi)
> > +{
> > + struct virtio_pstore *vps = psi->data;
> > + struct virtio_pstore_hdr *hdr = &vps->hdr;
> > + struct scatterlist sg[2];
> > + unsigned int flags = compressed ? VIRTIO_PSTORE_FL_COMPRESSED : 0;
> > +
> > + *id = vps->id++;
> > +
> > + hdr->cmd = cpu_to_virtio16(vps->vdev, VIRTIO_PSTORE_CMD_WRITE);
> > + hdr->id = cpu_to_virtio64(vps->vdev, *id);
> > + hdr->flags = cpu_to_virtio32(vps->vdev, flags);
> > + hdr->type = to_virtio_type(vps, type);
> > +
> > + sg_init_table(sg, 2);
> > + sg_set_buf(&sg[0], hdr, sizeof(*hdr));
> > + sg_set_buf(&sg[1], psi->buf, size);
> > + virtqueue_add_outbuf(vps->vq, sg, 2, vps, GFP_ATOMIC);
> > + virtqueue_kick(vps->vq);
> > +
> > + /* TODO: make it synchronous */
> > + return 0;
>
> The down side to this being asynchronous is the lack of error
> reporting. Perhaps this could check hdr->type before queuing and error
> for any VIRTIO_PSTORE_TYPE_UNKNOWN message instead of trying to send
> it?
I cannot follow, sorry. Could you please elaborate it more?
>
> > +}
> > +
> > +static int virt_pstore_erase(enum pstore_type_id type, u64 id, int count,
> > + struct timespec time, struct pstore_info *psi)
> > +{
> > + struct virtio_pstore *vps = psi->data;
> > + struct virtio_pstore_hdr *hdr = &vps->hdr;
> > + struct scatterlist sg[1];
> > + unsigned int len;
> > +
> > + hdr->cmd = cpu_to_virtio16(vps->vdev, VIRTIO_PSTORE_CMD_ERASE);
> > + hdr->id = cpu_to_virtio64(vps->vdev, id);
> > + hdr->type = to_virtio_type(vps, type);
> > +
> > + sg_init_one(sg, hdr, sizeof(*hdr));
> > + virtqueue_add_outbuf(vps->vq, sg, 1, vps, GFP_KERNEL);
> > + virtqueue_kick(vps->vq);
> > +
> > + wait_event(vps->acked, virtqueue_get_buf(vps->vq, &len));
> > + return 0;
> > +}
> > +
> > +static int virt_pstore_init(struct virtio_pstore *vps)
> > +{
> > + struct pstore_info *psinfo = &vps->pstore;
> > + int err;
> > +
> > + vps->id = 0;
> > + vps->buflen = 0;
> > + psinfo->bufsize = VIRT_PSTORE_BUFSIZE;
> > + psinfo->buf = (void *)__get_free_pages(GFP_KERNEL, VIRT_PSTORE_ORDER);
> > + if (!psinfo->buf) {
> > + pr_err("cannot allocate pstore buffer\n");
> > + return -ENOMEM;
> > + }
> > +
> > + psinfo->owner = THIS_MODULE;
> > + psinfo->name = "virtio";
> > + psinfo->open = virt_pstore_open;
> > + psinfo->close = virt_pstore_close;
> > + psinfo->read = virt_pstore_read;
> > + psinfo->erase = virt_pstore_erase;
> > + psinfo->write = virt_pstore_write;
> > + psinfo->flags = PSTORE_FLAGS_FRAGILE;
>
> For console support, this flag would need to be dropped -- though I
> suspect you know that already.:)
Yep, I intentionally support DMESG type only in this patchset for
simplicity. Others could be added later. :)
>
> > + psinfo->data = vps;
> > + spin_lock_init(&psinfo->buf_lock);
> > +
> > + err = pstore_register(psinfo);
> > + if (err)
> > + kfree(psinfo->buf);
> > +
> > + return err;
> > +}
[SNIP]
>
> Awesome! Can't wait to use it. :)
Thanks for your review! :)
Thanks,
Namhyung
>
> -Kees
>
> --
> Kees Cook
> Chrome OS & Brillo Security
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