From: "Michael S. Tsirkin" <mst@redhat.com>
To: Stefan Hajnoczi <stefanha@redhat.com>
Cc: kvm@vger.kernel.org, jasowang@redhat.com, cohuck@redhat.com,
slp@redhat.com, felipe@nutanix.com, john.g.johnson@oracle.com,
robert.bradford@intel.com, Dan Horobeanu <dhr@amazon.com>,
Stephen Barber <smbarber@chromium.org>,
Peter Shier <pshier@google.com>
Subject: Re: Proposal for MMIO/PIO dispatch file descriptors (ioregionfd)
Date: Mon, 24 Feb 2020 12:10:25 -0500 [thread overview]
Message-ID: <20200224120522-mutt-send-email-mst@kernel.org> (raw)
In-Reply-To: <20200222201916.GA1763717@stefanha-x1.localdomain>
On Sat, Feb 22, 2020 at 08:19:16PM +0000, Stefan Hajnoczi wrote:
> The KVM_IOREGIONFD_POSTED_WRITES flag
> skips waiting for an acknowledgement on write accesses. This is
> suitable for accesses that do not require synchronous emulation, such as
> doorbell register writes.
I would avoid hacks like this until we understand this better.
Specificlly one needs to be very careful since memory ordering semantics
can differ between a write into an uncacheable range and host writes into
a data structure. Reads from one region are also assumed to be ordered with
writes to another region, and drivers are known to make assumptions
like this.
Memory ordering being what it is, this isn't a field I'd be comfortable
device writes know what they are doing.
--
MST
next prev parent reply other threads:[~2020-02-24 17:10 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-02-22 20:19 Proposal for MMIO/PIO dispatch file descriptors (ioregionfd) Stefan Hajnoczi
2020-02-24 16:14 ` Christophe de Dinechin
2020-02-24 17:43 ` Stefan Hajnoczi
2020-02-24 17:10 ` Michael S. Tsirkin [this message]
2020-02-25 9:24 ` Stefan Hajnoczi
2020-02-25 11:57 ` Michael S. Tsirkin
2020-02-25 16:36 ` Stefan Hajnoczi
2020-02-25 12:19 ` Felipe Franciosi
2020-02-25 12:30 ` Felipe Franciosi
2020-02-25 16:47 ` Stefan Hajnoczi
2020-02-25 16:45 ` Stefan Hajnoczi
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