From: Milton Miller <miltonm@bga•com>
To: Alexander Graf <agraf@suse•de>
Cc: linuxppc-dev <linuxppc-dev@lists•ozlabs.org>,
Avi Kivity <avi@redhat•com>,
kvm-ppc@vger•kernel.org, KVM list <kvm@vger•kernel.org>
Subject: Re: [PATCH 26/26] KVM: PPC: Add Documentation about PV interface
Date: Mon, 28 Jun 2010 02:18:51 -0500 [thread overview]
Message-ID: <1277709531_13308@mail4.comsite.net> (raw)
In-Reply-To: <07C9A4B8-881A-438C-AA99-AEC23887C6B8@suse.de>
On Sun Jun 27 around 19:33:52 EST 2010 Alexander Graf wrote:
> Am 27.06.2010 um 10:14 schrieb Avi Kivity <avi at redhat.com>:
> > On 06/26/2010 02:25 AM, Alexander Graf wrote:
> > > +
> > > +PPC hypercalls
> > > +==============
> > > +
> > > +The only viable ways to reliably get from guest context to host
> > > context are:
> > > +
> > > + 1) Call an invalid instruction
> > > + 2) Call the "sc" instruction with a parameter to "sc"
> > > + 3) Call the "sc" instruction with parameters in GPRs
> > > +
> > > +Method 1 is always a bad idea. Invalid instructions can be
> > > replaced later on
> > > +by valid instructions, rendering the interface broken.
> > > +
> > > +Method 2 also has downfalls. If the parameter to "sc" is != 0 the
> > > spec is
> > > +rather unclear if the sc is targeted directly for the hypervisor
> > > or the
> > > +supervisor. It would also require that we read the syscall issuing
> > > instruction
> > > +every time a syscall is issued, slowing down guest syscalls.
> > > +
It goes to the hypervisor, and it would require the hypervisor to
return to the supervisor, but I believe it just returns to the user with
permission denied.
> > > +Method 3 is what KVM uses. We pass magic constants
> > > (KVM_SC_MAGIC_R3 and
> > > +KVM_SC_MAGIC_R4) in r3 and r4 respectively. If a syscall
> > > instruction with these
> > > +magic values arrives from the guest's kernel mode, we take the
> > > syscall as a
> > > +hypercall.
> > >
> >
> > Is there any chance a normal syscall will have those values in r3
> > and r4?
>
> r3 is the syscall number. So as long as the guest doesn't reuse that
> value, we're safe. Since in general syscall numbers are not randomly
> scattered throughout the number range, we should be ok here.
>
No, r0 has the system call number. Registers 3 and 4 are the first
2 args in c abi (or first 64 bit arg in 32 bit c abi), but the linux
syscall abi special. (In addition, it returns success or failure in
cr0).
> >
> > If so, maybe it's better to use pc as they key for hypercalls. Let
> > the guest designate one instruction address as the hypercall call
> > point; kvm can easily check it and reflect it back to the guest if
> > it doesn't match.
> >
>
> You mean the guest would tell the hv where the hypercall lies? That
> would require a hypercall, no? Defining it statically is tricky. I
> want to PV'nize osx using a kernel module later, so I don't have
> control over the physical layout.
>
> > Is it valid and useful to issue sc from privileged mode anyway,
> > except for calling the hypervisor?
>
> Same as a syscall on x86 really. The kernel can and does issue
> syscalls within itself.
>
>
I don't believe we support the kernel actually doing a syscall to itself
anymore, at least on powerpc. The callers call the underlying system
call function, or kernel_thread.
That said, I would suggest we allocate a syscall number for this, as it
would document the usage. (In additon to 0..nr_syscalls - 1 we have
0x1ebe in use).
Also, is there any desire to nest such emulation?
milton
next prev parent reply other threads:[~2010-06-28 7:19 UTC|newest]
Thread overview: 78+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-06-25 23:24 [PATCH 00/26] KVM PPC PV framework Alexander Graf
2010-06-25 23:24 ` [PATCH 01/26] KVM: PPC: Introduce shared page Alexander Graf
2010-06-27 12:12 ` Avi Kivity
2010-06-29 9:54 ` Alexander Graf
2010-06-29 10:55 ` Avi Kivity
2010-06-25 23:24 ` [PATCH 02/26] KVM: PPC: Convert MSR to " Alexander Graf
2010-06-27 8:16 ` Avi Kivity
2010-06-27 9:38 ` Alexander Graf
2010-06-27 9:50 ` Avi Kivity
2010-06-27 10:40 ` Alexander Graf
2010-06-25 23:24 ` [PATCH 03/26] KVM: PPC: Convert DSISR " Alexander Graf
2010-06-25 23:24 ` [PATCH 04/26] KVM: PPC: Convert DAR " Alexander Graf
2010-06-25 23:24 ` [PATCH 05/26] KVM: PPC: Convert SRR0 and SRR1 " Alexander Graf
2010-06-25 23:24 ` [PATCH 06/26] KVM: PPC: Convert SPRG[0-4] " Alexander Graf
2010-06-25 23:24 ` [PATCH 07/26] KVM: PPC: Implement hypervisor interface Alexander Graf
2010-06-25 23:24 ` [PATCH 08/26] KVM: PPC: Add PV guest critical sections Alexander Graf
2010-06-27 8:21 ` Avi Kivity
2010-06-27 9:40 ` Alexander Graf
2010-06-27 9:52 ` Avi Kivity
2010-06-27 10:33 ` Alexander Graf
2010-06-27 10:59 ` Avi Kivity
2010-06-27 11:49 ` Alexander Graf
2010-06-27 11:53 ` Avi Kivity
2010-06-27 12:06 ` Alexander Graf
2010-06-27 22:03 ` Benjamin Herrenschmidt
2010-06-27 10:03 ` Avi Kivity
2010-06-27 10:35 ` Alexander Graf
2010-06-25 23:24 ` [PATCH 09/26] KVM: PPC: Add PV guest scratch registers Alexander Graf
2010-06-27 8:22 ` Avi Kivity
2010-06-27 9:41 ` Alexander Graf
2010-06-27 9:53 ` Avi Kivity
2010-06-25 23:24 ` [PATCH 10/26] KVM: PPC: Tell guest about pending interrupts Alexander Graf
2010-06-25 23:24 ` [PATCH 11/26] KVM: PPC: Make RMO a define Alexander Graf
2010-06-26 16:52 ` Segher Boessenkool
2010-06-27 9:08 ` Alexander Graf
2010-06-29 7:32 ` Segher Boessenkool
2010-06-29 7:39 ` Alexander Graf
2010-06-29 7:52 ` Segher Boessenkool
2010-06-29 8:04 ` Alexander Graf
2010-06-25 23:25 ` [PATCH 12/26] KVM: PPC: First magic page steps Alexander Graf
2010-06-27 8:24 ` Avi Kivity
2010-06-27 9:44 ` Alexander Graf
2010-06-25 23:25 ` [PATCH 13/26] KVM: PPC: Magic Page Book3s support Alexander Graf
2010-06-25 23:25 ` [PATCH 14/26] KVM: PPC: Magic Page BookE support Alexander Graf
2010-06-25 23:25 ` [PATCH 15/26] KVM: PPC: Expose magic page support to guest Alexander Graf
2010-06-25 23:25 ` [PATCH 16/26] KVM: Move kvm_guest_init out of generic code Alexander Graf
2010-06-25 23:25 ` [PATCH 17/26] KVM: PPC: Generic KVM PV guest support Alexander Graf
2010-06-25 23:25 ` [PATCH 18/26] KVM: PPC: KVM PV guest stubs Alexander Graf
2010-06-27 8:28 ` Avi Kivity
2010-06-27 9:47 ` Alexander Graf
2010-06-27 10:16 ` Avi Kivity
2010-06-27 10:38 ` Alexander Graf
2010-06-27 22:04 ` Benjamin Herrenschmidt
2010-06-28 4:39 ` Matt Evans
2010-06-28 6:33 ` Alexander Graf
2010-06-28 8:15 ` Avi Kivity
2010-06-28 8:23 ` Alexander Graf
2010-06-28 8:33 ` Avi Kivity
2010-06-25 23:25 ` [PATCH 19/26] KVM: PPC: PV instructions to loads and stores Alexander Graf
2010-06-25 23:25 ` [PATCH 20/26] KVM: PPC: PV tlbsync to nop Alexander Graf
2010-06-25 23:25 ` [PATCH 21/26] KVM: PPC: Introduce kvm_tmp framework Alexander Graf
2010-06-25 23:25 ` [PATCH 22/26] KVM: PPC: PV assembler helpers Alexander Graf
2010-06-25 23:25 ` [PATCH 23/26] KVM: PPC: PV mtmsrd L=1 Alexander Graf
2010-06-25 23:25 ` [PATCH 24/26] KVM: PPC: PV mtmsrd L=0 and mtmsr Alexander Graf
2010-06-26 17:03 ` Segher Boessenkool
2010-06-27 9:10 ` Alexander Graf
2010-06-29 7:37 ` Segher Boessenkool
2010-06-25 23:25 ` [PATCH 25/26] KVM: PPC: PV wrteei Alexander Graf
2010-06-25 23:25 ` [PATCH 26/26] KVM: PPC: Add Documentation about PV interface Alexander Graf
2010-06-27 8:14 ` Avi Kivity
2010-06-27 9:33 ` Alexander Graf
2010-06-28 7:18 ` Milton Miller [this message]
2010-06-28 7:49 ` Alexander Graf
2010-06-28 8:13 ` Avi Kivity
2010-06-28 8:21 ` Alexander Graf
2010-06-28 8:32 ` Avi Kivity
2010-06-27 8:34 ` Avi Kivity
2010-06-27 9:49 ` Alexander Graf
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