Re: [virtio-dev] [PATCH] split-ring: Demand that a device must not change descriptor entries

[Rob Miller <rob.miller@broadcom.com>]

In reviewing my comments, I agree that I misunderstoodÂwhat was being requested. Please ignore my comments and continue as needed.

Rob Miller

rob.miller@broadcom.com

(919)721-3339

On Thu, Feb 27, 2020 at 5:05 AM Michael S. Tsirkin <mst@redhat.com> wrote:

On Mon, Nov 11, 2019 at 06:26:58PM +0100, Jan Kiszka wrote:
> On 11.11.19 18:17, Rob Miller wrote:
> > what is trying to be solvedÂhere? There is a reason why this is allowed
> > as some vendors update the table when using RX_MERABLE_BUFFERs &
> > F_IN_ORDER features
>
> OK, good to know. Which fields are updated then? Under which conditions (ie.
> in which states of the device)?
>
> The background is in the link below. My goal was to find a simple way
> declaring all fields read-only for the device to avoid problems with new
> implementations. But it looks like it's more complicated...
>
> Jan

No answer yet. Rob I see the following options:
- proceed with the ballot as is ignoring your comment. Maybe it's all a
 misunderstanding? It could be the comment was referring to the
 packed ring, where this patch refers to the split ring.
- make it weaker: MUST if PLATFORM_ACCESS is negotiated, and
 SHOULD if it isn't.

> >
> > Rob Miller
> > rob.miller@broadcom.com <mailto:rob.miller@broadcom.com>
> > (919)721-3339
> >
> >
> > On Mon, Nov 11, 2019 at 12:13 PM Jan Kiszka <jan.kiszka@siemens.com
> > <mailto:jan.kiszka@siemens.com>> wrote:
> >
> >Â Â ÂFrom: Jan Kiszka <jan.kiszka@siemens.com
> >Â Â Â<mailto:jan.kiszka@siemens.com>>
> >
> >Â Â ÂSo far the spec only indirectly says that a descriptor table entry is
> >Â Â Ânot modified by a device when processing it. Make this explicit by
> >Â Â Âadding it as normative requirement. Existing drivers already depend on
> >Â Â Âthis.
> >
> >Â Â ÂSee also
> >Â Â Âhttps://lists.oasis-open.org/archives/virtio-dev/201910/msg00057.html.
> >
> >Â Â ÂSigned-off-by: Jan Kiszka <jan.kiszka@siemens.com
> >Â Â Â<mailto:jan.kiszka@siemens.com>>
> >Â Â Â---
> >Â Â Â Âsplit-ring.tex | 2 +-
> >Â Â Â Â1 file changed, 1 insertion(+), 1 deletion(-)
> >
> >Â Â Âdiff --git a/split-ring.tex b/split-ring.tex
> >Â Â Âindex 123ac9f..bfef62d 100644
> >Â Â Â--- a/split-ring.tex
> >Â Â Â+++ b/split-ring.tex
> >Â Â Â@@ -217,7 +217,7 @@ \subsection{The Virtqueue Descriptor
> >Â Â ÂTable}\label{sec:Basic Facilities of a Virt
> >Â Â Â Â\devicenormative{\subsubsection}{The Virtqueue Descriptor
> >Â Â ÂTable}{Basic Facilities of a Virtio Device / Virtqueues / The
> >Â Â ÂVirtqueue Descriptor Table}
> >Â Â Â ÂA device MUST NOT write to a device-readable buffer, and a device
> >Â Â ÂSHOULD NOT
> >Â Â Â Âread a device-writable buffer (it MAY do so for debugging or
> >Â Â Âdiagnostic
> >Â Â Â-purposes).
> >Â Â Â+purposes). A device MUST NOT write to any descriptor table entry.
> >
> >Â Â Â Â\drivernormative{\subsubsection}{The Virtqueue Descriptor
> >Â Â ÂTable}{Basic Facilities of a Virtio Device / Virtqueues / The
> >Â Â ÂVirtqueue Descriptor Table}
> >Â Â Â ÂDrivers MUST NOT add a descriptor chain longer than $2^{32}$ bytes
> >Â Â Âin total;
> >Â Â Â--Â Â Â2.16.4
> >
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