From: "Jan Beulich" <JBeulich@suse.com>
To: Christopher Clark <christopher.w.clark@gmail.com>
Cc: Tim Deegan <tim@xen.org>,
Stefano Stabellini <sstabellini@kernel.org>,
Wei Liu <wei.liu2@citrix.com>,
ross.philipson@gmail.com, Jason Andryuk <jandryuk@gmail.com>,
Daniel Smith <dpsmith@apertussolutions.com>,
Andrew Cooper <andrew.cooper3@citrix.com>,
Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>,
Ian Jackson <Ian.Jackson@eu.citrix.com>,
Rich Persaud <persaur@gmail.com>,
James McKenzie <voreekf@madingley.org>,
George Dunlap <George.Dunlap@eu.citrix.com>,
Julien Grall <julien.grall@arm.com>,
Paul Durrant <paul.durrant@citrix.com>,
xen-devel <xen-devel@lists.xenproject.org>,
eric chanudet <eric.chanudet@gmail.com>
Subject: Re: [PATCH 16/25] argo: implement the notify op
Date: Thu, 20 Dec 2018 01:39:43 -0700 [thread overview]
Message-ID: <5C1B554F0200007800207E8B@prv1-mh.provo.novell.com> (raw)
In-Reply-To: <CACMJ4GYvsP7gDC+TeP0b9bWG+JRKhx0PV0fKD3inYYbRWuVzaA@mail.gmail.com>
>>> On 20.12.18 at 07:12, <christopher.w.clark@gmail.com> wrote:
> On Thu, Dec 13, 2018 at 6:06 AM Jan Beulich <JBeulich@suse.com> wrote:
>>
>> >>> On 01.12.18 at 02:32, <christopher.w.clark@gmail.com> wrote:
>> > +static uint32_t
>> > +argo_ringbuf_payload_space(struct domain *d, struct argo_ring_info *ring_info)
>> > +{
>> > + argo_ring_t ring;
>> > + int32_t ret;
>> > +
>> > + ASSERT(spin_is_locked(&ring_info->lock));
>> > +
>> > + ring.len = ring_info->len;
>> > + if ( !ring.len )
>> > + return 0;
>> > +
>> > + ring.tx_ptr = ring_info->tx_ptr;
>> > +
>> > + if ( argo_ringbuf_get_rx_ptr(ring_info, &ring.rx_ptr) )
>> > + return 0;
>> > +
>> > + argo_dprintk("argo_ringbuf_payload_space: tx_ptr=%d rx_ptr=%d\n",
>> > + ring.tx_ptr, ring.rx_ptr);
>> > +
>> > + if ( ring.rx_ptr == ring.tx_ptr )
>> > + return ring.len - sizeof(struct argo_ring_message_header);
>> > +
>> > + ret = ring.rx_ptr - ring.tx_ptr;
>> > + if ( ret < 0 )
>> > + ret += ring.len;
>>
>> Seeing these two if()-s - how is an empty ring distinguished from
>> a completely full one? I'm getting the impression that
>> ring.rx_ptr == ring.tx_ptr in both cases.
>
> The subtraction from ring.len above is missing an additional subtraction of
> ARGO_ROUNDUP(1), which doesn't help reasoning about this. (Fixed in v2.)
>
> If rx_ptr == tx_ptr, then the ring is empty. The ring insertion
> functions won't allow filling the ring, and I've added more comments
> in the v2 code to explain.
>
>> > + ret -= sizeof(struct argo_ring_message_header);
>> > + ret -= ARGO_ROUNDUP(1);
>>
>> Wouldn't you instead better round ret to a suitable multiple of
>> whatever granularity you try to arrange for here? Otherwise
>> what is this extra subtraction supposed to do?
>
> re: subtraction, have added new comment:
> /*
> * The maximum size payload for a message that will be accepted is:
> * (the available space between the ring indexes)
> * minus (space for a message header)
> * minus (space for one message slot)
> * since argo_ringbuf_insert requires that one message slot be left
> * unfilled, to avoid filling the ring to capacity and confusing a full
> * ring with an empty one.
> */
>
> re: rounding: Possibly. Not sure. In practice, both sides are
> updating the indexes in quantized steps matching the
> ARGO_ROUNDUP unit. Not sure it needs to change.
Here you appear to talk about both sides being well behaved. Did
you also consider misbehaving partners?
>> > +typedef struct argo_ring_data
>> > +{
>> > + uint64_t magic;
>>
>> What is this good for?
>
> New comment added:
> /*
> * Contents of the 'magic' field are inspected to verify that they contain
> * an expected value before the hypervisor will perform writes into this
> * structure in guest-supplied memory.
> */
But this does not help understand what this verification is good
for (or what it guards against). This again looks to be a reduction
of likelihood of misbehavior, instead of its exclusion.
As things accumulate: Personally I'd consider it better to wait
with posting a new version until discussions have settled. At
this point I'm already uncertain whether it'll be worthwhile for
me to thoroughly look at v2, when I'm likely to re-encounter
things I've already commented on in v1.
Jan
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next prev parent reply other threads:[~2018-12-20 8:39 UTC|newest]
Thread overview: 111+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-12-01 1:32 [PATCH 00/25] Argo: hypervisor-mediated interdomain communication Christopher Clark
2018-12-01 1:32 ` [PATCH 01/25] xen/evtchn: expose evtchn_bind_ipi_vcpu0_domain for use within Xen Christopher Clark
2018-12-03 16:20 ` Jan Beulich
2018-12-04 9:17 ` Christopher Clark
2018-12-01 1:32 ` [PATCH 02/25] argo: Introduce the Kconfig option to govern inclusion of Argo Christopher Clark
2018-12-03 15:51 ` Jan Beulich
2018-12-04 9:12 ` Christopher Clark
2018-12-01 1:32 ` [PATCH 03/25] argo: introduce the argo_message_op hypercall boilerplate Christopher Clark
2018-12-04 9:44 ` Paul Durrant
2018-12-20 5:13 ` Christopher Clark
2018-12-01 1:32 ` [PATCH 04/25] argo: define argo_dprintk for subsystem debugging Christopher Clark
2018-12-03 15:59 ` Jan Beulich
2018-12-01 1:32 ` [PATCH 05/25] argo: Add initial argo_init and argo_destroy Christopher Clark
2018-12-04 9:12 ` Paul Durrant
2018-12-13 13:16 ` Jan Beulich
2018-12-01 1:32 ` [PATCH 06/25] argo: Xen command line parameter 'argo': bool to enable/disable Christopher Clark
2018-12-04 9:18 ` Paul Durrant
2018-12-04 11:35 ` Jan Beulich
2018-12-01 1:32 ` [PATCH 07/25] xen (ARM, x86): add errno-returning functions for copy Christopher Clark
2018-12-04 9:35 ` Paul Durrant
2018-12-12 16:01 ` Roger Pau Monné
2018-12-20 5:16 ` Christopher Clark
2018-12-20 8:45 ` Jan Beulich
2018-12-20 12:57 ` Roger Pau Monné
2018-12-01 1:32 ` [PATCH 08/25] xen: define XEN_GUEST_HANDLE_NULL as null XEN_GUEST_HANDLE Christopher Clark
2018-12-04 11:39 ` Jan Beulich
2018-12-01 1:32 ` [PATCH 09/25] errno: add POSIX error codes EMSGSIZE, ECONNREFUSED to the ABI Christopher Clark
2018-12-03 15:42 ` Jan Beulich
2018-12-04 9:10 ` Christopher Clark
2018-12-04 10:04 ` Jan Beulich
2018-12-01 1:32 ` [PATCH 10/25] arm: introduce guest_handle_for_field() Christopher Clark
2018-12-04 9:46 ` Paul Durrant
2018-12-01 1:32 ` [PATCH 11/25] xsm, argo: XSM control for argo register operation, argo_mac bootparam Christopher Clark
2018-12-04 9:52 ` Paul Durrant
2018-12-20 5:19 ` Christopher Clark
2018-12-01 1:32 ` [PATCH 12/25] xsm, argo: XSM control for argo message send operation Christopher Clark
2018-12-04 9:53 ` Paul Durrant
2018-12-01 1:32 ` [PATCH 13/25] argo: implement the register op Christopher Clark
2018-12-02 20:10 ` Julien Grall
2018-12-04 9:08 ` Christopher Clark
2018-12-05 17:20 ` Julien Grall
2018-12-05 22:35 ` Christopher Clark
2018-12-11 13:51 ` Julien Grall
2018-12-04 10:57 ` Paul Durrant
2018-12-12 9:48 ` Jan Beulich
2018-12-20 5:29 ` Christopher Clark
2018-12-20 8:29 ` Jan Beulich
2018-12-21 1:25 ` Christopher Clark
2018-12-21 7:28 ` Jan Beulich
2018-12-21 8:16 ` Christopher Clark
2018-12-21 8:53 ` Jan Beulich
2018-12-21 23:28 ` Christopher Clark
2018-12-12 16:47 ` Roger Pau Monné
2018-12-20 5:41 ` Christopher Clark
2018-12-20 8:51 ` Jan Beulich
2018-12-20 12:52 ` Roger Pau Monné
2018-12-21 23:05 ` Christopher Clark
2019-01-04 8:57 ` Roger Pau Monné
2019-01-04 13:22 ` Jan Beulich
2019-01-04 15:35 ` Roger Pau Monné
2019-01-04 15:47 ` Jan Beulich
2019-01-07 9:00 ` Roger Pau Monné
2019-01-09 16:15 ` Tamas K Lengyel
2019-01-09 16:23 ` Razvan Cojocaru
2019-01-09 16:34 ` Roger Pau Monné
2019-01-09 16:48 ` Razvan Cojocaru
2019-01-09 16:50 ` Tamas K Lengyel
2019-01-09 16:59 ` Roger Pau Monné
2019-01-09 17:03 ` Fwd: " Roger Pau Monné
2019-01-09 17:03 ` Razvan Cojocaru
2018-12-01 1:32 ` [PATCH 14/25] argo: implement the unregister op Christopher Clark
2018-12-04 11:10 ` Paul Durrant
2018-12-12 9:51 ` Jan Beulich
2018-12-01 1:32 ` [PATCH 15/25] argo: implement the sendv op Christopher Clark
2018-12-04 11:22 ` Paul Durrant
2018-12-12 11:52 ` Jan Beulich
2018-12-20 5:58 ` Christopher Clark
2018-12-20 8:33 ` Jan Beulich
2019-01-04 8:13 ` Christopher Clark
2019-01-04 8:43 ` Roger Pau Monné
2019-01-04 13:37 ` Jan Beulich
2019-01-07 20:54 ` Christopher Clark
2018-12-01 1:32 ` [PATCH 16/25] argo: implement the notify op Christopher Clark
2018-12-13 14:06 ` Jan Beulich
2018-12-20 6:12 ` Christopher Clark
2018-12-20 8:39 ` Jan Beulich [this message]
2018-12-01 1:32 ` [PATCH 17/25] xsm, argo: XSM control for any access to argo by a domain Christopher Clark
2018-12-01 1:32 ` [PATCH 18/25] argo: limit the max number of rings that a domain may register Christopher Clark
2018-12-13 14:08 ` Jan Beulich
2018-12-01 1:32 ` [PATCH 19/25] argo: limit the max number of notify requests in a single operation Christopher Clark
2018-12-01 1:32 ` [PATCH 20/25] argo, xsm: notify: don't describe rings that cannot be sent to Christopher Clark
2018-12-01 1:33 ` [PATCH 21/25] argo: add array_index_nospec to guard the result of the hash func Christopher Clark
2018-12-13 14:10 ` Jan Beulich
2018-12-01 1:33 ` [PATCH 22/25] xen/evtchn: expose send_guest_global_virq for use within Xen Christopher Clark
2018-12-13 14:12 ` Jan Beulich
2018-12-01 1:33 ` [PATCH 23/25] argo: signal x86 HVM and ARM via VIRQ Christopher Clark
2018-12-02 19:55 ` Julien Grall
2018-12-04 9:03 ` Christopher Clark
2018-12-04 9:16 ` Paul Durrant
2018-12-12 14:49 ` James
2018-12-11 14:15 ` Julien Grall
2018-12-13 14:16 ` Jan Beulich
2018-12-20 6:20 ` Christopher Clark
2018-12-01 1:33 ` [PATCH 24/25] argo: unmap rings on suspend and send signal to ring-owners on resume Christopher Clark
2018-12-13 14:26 ` Jan Beulich
2018-12-20 6:25 ` Christopher Clark
2018-12-01 1:33 ` [PATCH 25/25] argo: implement the get_config op to query notification config Christopher Clark
2018-12-13 14:32 ` Jan Beulich
2018-12-03 16:49 ` [PATCH 00/25] Argo: hypervisor-mediated interdomain communication Chris Patterson
2018-12-04 9:00 ` Christopher Clark
2018-12-11 22:13 ` Chris Patterson
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