On Thu, Oct 27, 2016 at 12:45 AM, Andrew Cooper <andrew.coop...@citrix.com> wrote:
> On 26/10/2016 20:37, Matt Leinhos wrote: > > A while ago there was a thread by the same name in this group (see > > https://lists.xen.org/archives/html/xen-devel/2016-08/msg02591.html). > > > > I've looked through the thread and did not see a resolution: do we have > > an example handler for #VE - preferably on x86_64? I haven't found such > > a handler in the xen code or through searches. > > > > I am attempting to use the altp2m API from a domU and need to handle #VE. > > A #VE handler is only interesting for a domU, knowing it is running > under an altp2m-capable hypervisor. > > The hypervisor itself won't ever receive #VE from real hardware, which > is why there is no example code in Xen. > Well, unless Xen is running in a nested setting ;) > > I don't know if there is any public example code, but a #VE handler in > domU is intended to work very similarly to a plain #PF handler. #VE > specifically means "there is an EPT translation but the access failed > for permission reasons, and the guest has elected to handle this fault > itself". It is then up to the domU kernel to decide what to do; whether > to terminate the process/thread which cause the violation, or to alter > the permissions and rerun the instruction. > Correct. The guest itself needs to issue the appropriate HVMOP hypercalls to enable #VE and register the memory location where the trap info should be stored at. The only caveat is that only permission faults in altp2m view 1-10 will generate a #VE in the domU, view 0 won't (at least when it is emulated on hw without real #VE support). Tamas
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