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Re: [Qemu-ppc] [PATCH] spapr: add "compat" machine option

From: Alexander Graf
Subject: Re: [Qemu-ppc] [PATCH] spapr: add "compat" machine option
Date: Mon, 30 Sep 2013 16:49:52 +0200
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:10.0.3) Gecko/20120306 Thunderbird/10.0.3

On 09/30/2013 03:22 PM, Alexey Kardashevskiy wrote:
On 30.09.2013 21:25, Alexander Graf wrote:
On 27.09.2013, at 10:06, Alexey Kardashevskiy wrote:

To be able to boot on newer hardware that the software support,
PowerISA defines a logical PVR, one per every PowerISA specification
version from 2.04.

This adds the "compat" option which takes values 205 or 206 and forces
QEMU to boot the guest with a logical PVR (CPU_POWERPC_LOGICAL_2_05 or

The guest reads the logical PVR value from "cpu-version" property of
a CPU device node.

Cc: Nikunj A Dadhania<address@hidden>
Cc: Andreas Färber<address@hidden>
Signed-off-by: Alexey Kardashevskiy<address@hidden>
hw/ppc/spapr.c          | 40 ++++++++++++++++++++++++++++++++++++++++
include/hw/ppc/spapr.h  |  2 ++
target-ppc/cpu-models.h | 10 ++++++++++
target-ppc/cpu.h        |  3 +++
target-ppc/kvm.c        |  2 ++
vl.c                    |  4 ++++
6 files changed, 61 insertions(+)

diff --git a/hw/ppc/spapr.c b/hw/ppc/spapr.c
index a09a1d9..737452d 100644
--- a/hw/ppc/spapr.c
+++ b/hw/ppc/spapr.c
@@ -33,6 +33,7 @@
#include "sysemu/kvm.h"
#include "kvm_ppc.h"
#include "mmu-hash64.h"
+#include "cpu-models.h"

#include "hw/boards.h"
#include "hw/ppc/ppc.h"
@@ -196,6 +197,26 @@ static XICSState *xics_system_init(int nr_servers, int 
     return icp;

+static void spapr_compat_mode_init(sPAPREnvironment *spapr)
+    QemuOpts *machine_opts = qemu_get_machine_opts();
+    uint64_t compat = qemu_opt_get_number(machine_opts, "compat", 0);
+    switch (compat) {
+    case 0:
+        break;
+    case 205:
+        spapr->arch_compat = CPU_POWERPC_LOGICAL_2_05;
+        break;
+    case 206:
+        spapr->arch_compat = CPU_POWERPC_LOGICAL_2_06;
Does it make sense to declare compat mode a number or would a string
be easier for users? I can imagine that "-machine compat=power6" is
easier to understand for a user than "-machine compat=205".
I just follow the PowerISA spec. It does not say anywhere (at least I do
not see it) that 2.05==power6. 2.05 was released when power6 was
released and power6 supports 2.05 but these are not synonims. And
"compat=power6" would not set "cpu-version" to any of power6 PVRs, it
still will be a logical PVR. It confuses me too to tell qemu "205"
instead of "power6" but it is the spec to blame :)

So what is "2_06 plus" then? :)

To me it really sounds like a 1:1 mapping to cores rather than specs - the ISA defines a lot more capabilities than a single core necessarily supports, especially with the inclusion of booke into the generic ppc spec.

+        break;
+    default:
+        perror("Unsupported mode, only are 205, 206 supported\n");
+        break;
+    }
static int spapr_fixup_cpu_dt(void *fdt, sPAPREnvironment *spapr)
     int ret = 0, offset;
@@ -206,6 +227,7 @@ static int spapr_fixup_cpu_dt(void *fdt, sPAPREnvironment 

     CPU_FOREACH(cpu) {
         DeviceClass *dc = DEVICE_GET_CLASS(cpu);
+        CPUPPCState *env =&(POWERPC_CPU(cpu)->env);
         uint32_t associativity[] = {cpu_to_be32(0x5),
@@ -238,6 +260,14 @@ static int spapr_fixup_cpu_dt(void *fdt, sPAPREnvironment 
         if (ret<  0) {
             return ret;
+        if (env->arch_compat) {
+            ret = fdt_setprop(fdt, offset, "cpu-version",
+&env->arch_compat, sizeof(env->arch_compat));
+            if (ret<  0) {
+                return ret;
+            }
+        }
     return ret;
@@ -1145,6 +1175,8 @@ static void ppc_spapr_init(QEMUMachineInitArgs *args)
     spapr = g_malloc0(sizeof(*spapr));

+    spapr_compat_mode_init(spapr);
     cpu_ppc_hypercall = emulate_spapr_hypercall;

     /* Allocate RMA if necessary */
@@ -1226,6 +1258,14 @@ static void ppc_spapr_init(QEMUMachineInitArgs *args)

         xics_cpu_setup(spapr->icp, cpu);

+        /*
+         * If compat mode is set in the command line, pass it to CPU so KVM
+         * will be able to set it in the host kernel.
+         */
+        if (spapr->arch_compat) {
+            env->arch_compat = spapr->arch_compat;
You should set the compat mode in KVM here, rather than doing it in
the put_registers call which gets invoked on every register sync. Or can
the guest change the mode?

I will change it here in the next patch (which requires kernel changes
which are not there yet). The guest cannot change it directly but it can
indirectly via "client-architecture-support".

They probably want a generic callback then. What happens on reset?

Also, we need to handle failure. If the kernel can not set the CPU
2.05 mode for example (IIRC POWER8 doesn't allow you to) we should bail
out here.

Yep, I'll add this easy check :)

And then there's the TCG question. We either have to disable CPU
features similar to how we handle it in KVM (by setting and honoring the
respective bits in PCR) or we need to bail out too and declare compat
mode unsupported for TCG.

At the moment we want to run old distro on new CPUs. This patch would
make more sense with the "ibm,client-architecture-support" and "power8
registers migration" patches which I did not post yet.

Disabling "unsupported" bits in TCG would be really nice indeed and we
should eventually do this but 1) it will not really hurt the guest if we
did not disable some feature (really old guest will not use it and
that's it)  2) once created, PowerPCCPUState (or whatever the exact name
is, I am writing this mail on windows machine :) ) is not very flexible
to reconfigure...

Can't you just set the bits in PCR and add an XXX comment indicating that we're currently not honoring them? Then fron the machine code point of view, everything is implemented.

And then there's the fact that the kernel interface isn't upstream in a way that
? unfinished sentence? What is missing in the kernel right now?

Eh. I think I wanted to say that this depends on in-kernel patches that are not upstream yet :).

+        }
         qemu_register_reset(spapr_cpu_reset, cpu);

diff --git a/include/hw/ppc/spapr.h b/include/hw/ppc/spapr.h
index ca175b0..201c578 100644
--- a/include/hw/ppc/spapr.h
+++ b/include/hw/ppc/spapr.h
@@ -34,6 +34,8 @@ typedef struct sPAPREnvironment {
     uint32_t epow_irq;
     Notifier epow_notifier;

+    uint32_t arch_compat;        /* Compatible PVR from the command line */
     /* Migration state */
     int htab_save_index;
     bool htab_first_pass;
diff --git a/target-ppc/cpu-models.h b/target-ppc/cpu-models.h
index 49ba4a4..d7c033c 100644
--- a/target-ppc/cpu-models.h
+++ b/target-ppc/cpu-models.h
@@ -583,6 +583,16 @@ enum {
     CPU_POWERPC_RS64II             = 0x00340000,
     CPU_POWERPC_RS64III            = 0x00360000,
     CPU_POWERPC_RS64IV             = 0x00370000,
+    /* Logical CPUs */
+    CPU_POWERPC_LOGICAL_2_04       = 0x0F000001,
+    CPU_POWERPC_LOGICAL_2_05       = 0x0F000002,
+    CPU_POWERPC_LOGICAL_2_06       = 0x0F000003,
+    CPU_POWERPC_LOGICAL_2_06_PLUS  = 0x0F100003,
+    CPU_POWERPC_LOGICAL_2_07       = 0x0F000004,
+    CPU_POWERPC_LOGICAL_2_08       = 0x0F000005,
These don't really belong here.

Sorry, I do not understand. These are PVRs which are used in
"cpu-version" DT property. They are logical PVRs but still PVRs - i.e.
the guest has PVR masks for them too.

But they are specific to PAPR, not PowerPC in general, no? And you would never find one in the PVR register of a guest.

#endif /* defined(TARGET_PPC64) */
     /* Original POWER */
     /* XXX: should be POWER (RIOS), RSC3308, RSC4608,
diff --git a/target-ppc/cpu.h b/target-ppc/cpu.h
index 422a6bb..fc837c1 100644
--- a/target-ppc/cpu.h
+++ b/target-ppc/cpu.h
@@ -999,6 +999,9 @@ struct CPUPPCState {
     /* Device control registers */
     ppc_dcr_t *dcr_env;

+    /* Architecture compatibility mode */
+    uint32_t arch_compat;

Do we really need to carry this in the vcpu struct? Or can we just
fire-and-forget about it? If we want to preserve anything, it should
be the PCR register.
This is the current PVR value aka "cpu-version" property. It may change
during reboots as every reboot does the "client-architecture-support"
call so the logical PVR can change.

Ok, so again: What happens on reset / reboot? Do we want to preserve the compatibility setting or does that get reset as well?


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