On Thursday 03 September 2015 07:32 AM, Paul Mackerras wrote: > On Sun, Aug 09, 2015 at 03:53:02PM +0200, Alexander Graf wrote: >> >> >> On 07.08.15 05:37, Sam Bobroff wrote: >>> The RTAS call being discussed in this thread actually has two vectors to >>> patch >>> (System Reset and Machine Check), and the patches so far only address the >>> Machine Check part. I've been looking at filling in the System Reset part >>> and >>> that will mean basing my code on top of this set. I would like to keep the >>> same style of solution for both vectors, so I'd like to get the discussion >>> started again :-) >>> >>> So (1) do we use a trampoline in guest memory, and if so (2) how is the >>> trampoline code handled? >>> >>> (1) It does seem simpler to me to deliver directly to the handler, but I'm >>> worried about a few things: >>> >>> If a guest were to call ibm,nmi-register and then kexec to a new kernel that >>> does not call ibm,nmi-register, would the exception cause a jump to a stale >>> address? >> >> Probably - how does that get handled today with pHyp? Does pHyp just >> override the actual exception vector code and thus the kexec'ed code >> path gets overwritten? >> >> I don't remember the original patch set fully, but if all we need is to >> override 0x200, why can't we replace the code with >> >> mtsprg scratch, r0 >> li r0, HCALL_KVM_MC >> sc 1 >> >> then there is no complexity in that code at all with dynamically patched >> bits. Or am I missing the obvious? > > Well, sc 1 will overwrite SRR0/1, and as far as I can see SRR0/1 have > the only record of where the machine check occurred. So we can't use > sc 1 unless we first save SRR0/1 somewhere. We could instead use some > specific illegal instruction, which will cause a hypervisor emulation > assist interrupt using HSRR0/1.
I now see that I am not saving SRR0/1 which contains information (nip, msr) on machine check in 0x200 vector. I am restoring SRR0/1 in the private hcall h_report_mc_err() which is wrong: ... + CPUPPCState *env = &cpu->env; ... + mc_log.srr0 = env->spr[SPR_SRR0]; + mc_log.srr1 = env->spr[SPR_SRR1]; ... SRR0/1 above contains the values at the time when private hcall is invoked, not the values at the time when machine check exception occurred. Regards, Aravinda > > Paul. > -- Regards, Aravinda
