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Re: [RFC v2 00/14] Add SDEI support for arm64
Re: [RFC v2 00/14] Add SDEI support for arm64
Tue, 4 Feb 2020 16:26:20 +0800
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Update Marc's email address.
+cc Gavin as he is posting a RFC for ARM NMI.
Really sorry for missing to update your email address, for the initial
topic was raised long time ago and I forgot to update the Cc list in the
commit message of the patches.
Thanks Gavin for forwarding current discussion on ARM NMI to me.
For you said SDEI is "horrible", does it mean we'd better never
implement SDEI in virtual world? Or do you have any advice on how to
On 2019/12/23 16:20, Guoheyi wrote:
Really appreciate your comments.
For other platforms/boards emulated in qemu, like omap, imx*, etc, are
they just TCG platforms? Can we just enable security and EL3 emulation
for these platforms instead of implementing copies of firmware
interfaces in qemu? Also I think it is possible to optimize the code
to support all KVM enabled virtual boards with one single copy of SDEI
code, so at least the duplication of code inside qemu might be avoided.
I can understand your concerns; the exsiting SDEI code in ARM Trusted
Firmware also tempted me when I started to writing the code in qemu. I
agree the ideal way is to use the existing firmware directly, but how
can we achieve that? Either I don't think it is good to modify the
firmware code too much, for firmware should be kept simple and reliable.
Does James or Marc have any idea?
在 2019/12/20 21:44, Peter Maydell 写道:
On Tue, 5 Nov 2019 at 09:12, Heyi Guo <address@hidden> wrote:
SDEI is for ARM "Software Delegated Exception Interface". AS ARM64
native non-maskable interrupt (NMI), we rely on higher privileged
exception level) software to change the execution flow of lower
(smaller exception level) software when certain events occur, to
mechanism, and SDEI is the standard interfaces between the two
privileged software. It is based on SMC/HVC calls.
The higher privileged software implements an SDEI dispatcher to
related SMC/HVC calls and trigger SDEI events; the lower privileged
implements an SDEI client to request SDEI services and handle SDEI
Hi; I read through these patches last week, but I didn't reply
then because although there are some aspects to the design that
I don't like, I don't have a clear idea of what a better approach
to the problems it's trying to solve would be. However I didn't
want to go home for the end of the year without providing at
least some response. So I'm going to lay out the parts I have
issues with and perhaps somebody else will have a good idea.
The first part that I dislike here is that this is implementing
an entire ABI which in real hardware is provided by firmware. I
think that QEMU's design works best when QEMU provides emulation of
hardware or hardware-like facilities, which guest code (either
in the kernel, or firmware/bios running in the guest) can then
make use of. Once we start getting into implementing firmware
interfaces directly in QEMU this rapidly becomes a large amount
of work and code, and it's unclear where it should stop. Should
we implement also the equivalent of firmware for omap boards?
For imx* boards? For the raspberry pi? For xilinx boards?
Are we going to end up reimplementing more of ARM Trusted Firmware
functionality inside QEMU? The code to implement firmware-equivalent
ABIs in all these boards would I think quickly become a large part
of the codebase.
My second concern is that to do the things it wants to do,
the implementation here does some pretty invasive things:
* intercepting interrupt lines which ought to just be
emulated hardware signals between devices and the GIC
* capturing register values of other CPUs, and arbitrarily
stopping those other CPUs and making them run other code
at a later point in time
I'm really uncomfortable with what's just an 'emulated firmware'
interface for one specific board model doing this kind of thing.
Finally, the stated rationale for the patchset ("we'd like an
emulated NMI equivalent") doesn't really feel to me like it's
strong enough to counterbalance the amount of code here and
the degree to which it's moving us into a swamp I'd prefer
it if we could stay out of.
I'd be much happier with a design where QEMU provides simple
facilities to the guest and the guest firmware and kernel
deal with making use of them. I appreciate that it's not
clear how that would work though, given that in real hardware
this works by the firmware running at EL3 and KVM not
providing a mechanism that allows guest code that runs at
a higher (effective or emulated) privilege level than the
- Re: [RFC v2 00/14] Add SDEI support for arm64,
Heyi Guo <=