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Date: Tue, 18 Jun 2019 06:47:01 -0500
From: Segher Boessenkool <segher@kernel.crashing.org>
To: Paul Mackerras <paulus@ozlabs.org>
Subject: Re: [PATCH v3 4/9] KVM: PPC: Ultravisor: Add generic ultravisor call
 handler
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References: <20190606173614.32090-1-cclaudio@linux.ibm.com>
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Cc: Madhavan Srinivasan <maddy@linux.vnet.ibm.com>,
 Michael Anderson <andmike@linux.ibm.com>, Ram Pai <linuxram@us.ibm.com>,
 Claudio Carvalho <cclaudio@linux.ibm.com>, kvm-ppc@vger.kernel.org,
 Bharata B Rao <bharata@linux.ibm.com>, linuxppc-dev@ozlabs.org,
 Sukadev Bhattiprolu <sukadev@linux.vnet.ibm.com>,
 Thiago Bauermann <bauermann@linux.ibm.com>,
 Anshuman Khandual <khandual@linux.vnet.ibm.com>
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 <linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org>

Hi Paul,

On Mon, Jun 17, 2019 at 12:06:32PM +1000, Paul Mackerras wrote:
> The thing we need to consider is that when SMFCTRL[E] = 0, a ucall
> instruction becomes a hcall (that is, sc 2 is executed as if it was
> sc 1).  In that case, the first argument to the ucall will be
> interpreted as the hcall number.  Mostly that will happen not to be a
> valid hcall number, but sometimes it might unavoidably be a valid but
> unintended hcall number.

Shouldn't a caller of the ultravisor *know* that it is talking to the
ultravisor in the first place?  And not to the hypervisor.


Segher