Re: [Qemu-devel] [PATCH v2 8/9] spapr: Implement processor compatibility in ibm, client-architecture-support

[Alexey Kardashevskiy <aik@ozlabs.ru>]

On 05/21/2014 07:21 PM, Alexander Graf wrote:
> 
> On 21.05.14 10:27, Alexey Kardashevskiy wrote:
>> Modern Linux kernels support last POWERPC CPUs so when a kernel boots,
>> in most cases it can find a matching cpu_spec in the kernel's cpu_specs
>> list. However if the kernel is quite old, it may be missing a definition
>> of the actual CPU. To provide an ability for old kernels to work on modern
>> hardware, a Processor Compatibility Mode has been introduced
>> by the PowerISA specification.
>>
>>  From the hardware prospective, it is supported by the Processor
>> Compatibility Register (PCR) which is defined in PowerISA. The register
>> enables one of the compatibility modes (2.05/2.06/2.07).
>> Since PCR is a hypervisor privileged register and cannot be
>> directly accessed from the guest, the mode selection is done via
>> ibm,client-architecture-support (CAS) RTAS call using which the guest
>> specifies what "raw" and "architected" CPU versions it supports.
>> QEMU works out the best match, changes a "cpu-version" property of
>> every CPU and notifies the guest about the change by setting these
>> properties in the buffer passed as a response on a custom H_CAS hypercall.
>>
>> This implements ibm,client-architecture-support parameters parsing
>> (now only for PVRs) and cooks the device tree diff with new values for
>> "cpu-version", "ibm,ppc-interrupt-server#s" and
>> "ibm,ppc-interrupt-server#s" properties.
>>
>> Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>
>> ---
>>   hw/ppc/spapr.c       |  4 ++-
>>   hw/ppc/spapr_hcall.c | 85
>> ++++++++++++++++++++++++++++++++++++++++++++++++++++
>>   trace-events         |  4 +++
>>   3 files changed, 92 insertions(+), 1 deletion(-)
>>
>> diff --git a/hw/ppc/spapr.c b/hw/ppc/spapr.c
>> index 14c72d9..020426a 100644
>> --- a/hw/ppc/spapr.c
>> +++ b/hw/ppc/spapr.c
>> @@ -34,6 +34,7 @@
>>   #include "sysemu/kvm.h"
>>   #include "kvm_ppc.h"
>>   #include "mmu-hash64.h"
>> +#include "qom/cpu.h"
>>     #include "hw/boards.h"
>>   #include "hw/ppc/ppc.h"
>> @@ -601,7 +602,8 @@ int spapr_h_cas_compose_response(target_ulong addr,
>> target_ulong size)
>>       _FDT((fdt_open_into(fdt_skel, fdt, size)));
>>       g_free(fdt_skel);
>>   -    /* Place to make changes to the tree */
>> +    /* Fix skeleton up */
>> +    _FDT((spapr_fixup_cpu_dt(fdt, spapr)));
>>         /* Pack resulting tree */
>>       _FDT((fdt_pack(fdt)));
>> diff --git a/hw/ppc/spapr_hcall.c b/hw/ppc/spapr_hcall.c
>> index 2f6aa5c..2e0a49c 100644
>> --- a/hw/ppc/spapr_hcall.c
>> +++ b/hw/ppc/spapr_hcall.c
>> @@ -3,6 +3,9 @@
>>   #include "helper_regs.h"
>>   #include "hw/ppc/spapr.h"
>>   #include "mmu-hash64.h"
>> +#include "cpu-models.h"
>> +#include "trace.h"
>> +#include "kvm_ppc.h"
>>     struct SPRSyncState {
>>       CPUState *cs;
>> @@ -752,12 +755,94 @@ out:
>>       return ret;
>>   }
>>   +#define get_compat_level(cpuver) ( \
>> +    ((cpuver) == CPU_POWERPC_LOGICAL_2_05) ? 2050 : \
>> +    ((cpuver) == CPU_POWERPC_LOGICAL_2_06) ? 2060 : \
>> +    ((cpuver) == CPU_POWERPC_LOGICAL_2_06_PLUS) ? 2061 : \
>> +    ((cpuver) == CPU_POWERPC_LOGICAL_2_07) ? 2070 : 0)
>> +
>>   static target_ulong h_client_architecture_support(PowerPCCPU *cpu_,
>>                                                     sPAPREnvironment *spapr,
>>                                                     target_ulong opcode,
>>                                                     target_ulong *args)
>>   {
>>       target_ulong list = args[0];
>> +    PowerPCCPUClass *pcc_ = POWERPC_CPU_GET_CLASS(cpu_);
>> +    CPUState *cs;
>> +    bool cpu_match = false;
>> +    unsigned old_cpu_version = cpu_->cpu_version;
>> +    unsigned compat_lvl = 0, cpu_version = 0;
>> +    unsigned max_lvl = get_compat_level(cpu_->max_compat);
>> +
>> +    /* Parse PVR list */
>> +    for ( ; ; ) {
>> +        uint32_t pvr, pvr_mask;
>> +
>> +        pvr_mask = rtas_ld(list, 0);
>> +        list += 4;
>> +        pvr = rtas_ld(list, 0);
>> +        list += 4;
>> +
>> +        trace_spapr_cas_pvr_try(pvr);
>> +        if (!max_lvl &&
>> +            ((cpu_->env.spr[SPR_PVR] & pvr_mask) == (pvr & pvr_mask))) {
>> +            cpu_match = true;
>> +            cpu_version = 0;
>> +        } else if (pvr == cpu_->cpu_version) {
>> +            cpu_match = true;
>> +            cpu_version = cpu_->cpu_version;
>> +        } else if (!cpu_match) {
>> +            /* If it is a logical PVR, try to determine the highest
>> level */
>> +            unsigned lvl = get_compat_level(pvr);
>> +            if (lvl) {
>> +                bool is205 = (pcc_->pcr_mask & PCR_COMPAT_2_05) &&
>> +                     (lvl == get_compat_level(CPU_POWERPC_LOGICAL_2_05));
>> +                bool is206 = (pcc_->pcr_mask & PCR_COMPAT_2_06) &&
>> +                    ((lvl == get_compat_level(CPU_POWERPC_LOGICAL_2_06)) ||
>> +                    (lvl ==
>> get_compat_level(CPU_POWERPC_LOGICAL_2_06_PLUS)));
>> +
>> +                if (is205 || is206) {
>> +                    if (!max_lvl) {
>> +                        /* User did not set the level, choose the
>> highest */
>> +                        if (compat_lvl <= lvl) {
>> +                            compat_lvl = lvl;
>> +                            cpu_version = pvr;
>> +                        }
>> +                    } else if (max_lvl >= lvl) {
>> +                        /* User chose the level, don't set higher than
>> this */
>> +                        compat_lvl = lvl;
>> +                        cpu_version = pvr;
>> +                    }
>> +                }
>> +            }
>> +        }
>> +        /* Terminator record */
>> +        if (~pvr_mask & pvr) {
> 
> This loop can be used by the guest to stall QEMU for a long period of time,
> no? Better add a safety net check somewhere to allow for early abort.

Like what? No more than 64 PVRs would be enough?



>> +            break;
>> +        }
>> +    }
>> +
>> +    /* For the future use: here @list points to the first capability */
>> +
>> +    /* Parsing finished */
>> +    trace_spapr_cas_pvr(cpu_->cpu_version, cpu_match,
>> +                        cpu_version, pcc_->pcr_mask);
>> +
>> +    /* Update CPUs */
>> +    if (old_cpu_version != cpu_version) {
>> +        CPU_FOREACH(cs) {
>> +            PowerPCCPU *cpu = POWERPC_CPU(cs);
>> +
>> +            if (ppc_set_compat(cpu, cpu_version) < 0) {
> 
> Please run the updates on the vcpu threads themselves.

Ouch. Forgot. Sorry :(


-- 
Alexey