From: Thomas Huth <thuth@redhat.com>
To: David Gibson <david@gibson.dropbear.id.au>
Cc: qemu-ppc@nongnu.org, qemu-devel@nongnu.org, laurent@vivier.eu
Subject: Re: [Qemu-devel] [PATCH 1/4] hw/ppc/spapr: Add h_set_sprg0 hypercall
Date: Thu, 11 Feb 2016 08:12:54 +0100 [thread overview]
Message-ID: <56BC3476.6090700@redhat.com> (raw)
In-Reply-To: <20160210233020.GE29288@voom.bne.redhat.com>
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On 11.02.2016 00:30, David Gibson wrote:
> On Wed, Feb 10, 2016 at 07:09:09PM +0100, Thomas Huth wrote:
>> This is a very simple hypercall that only sets up the SPRG0
>> register for the guest (since writing to SPRG0 was only permitted
>> to the hypervisor in older versions of the PowerISA).
>>
>> Signed-off-by: Thomas Huth <thuth@redhat.com>
>> ---
>> hw/ppc/spapr_hcall.c | 15 +++++++++++++--
>> 1 file changed, 13 insertions(+), 2 deletions(-)
>>
>> diff --git a/hw/ppc/spapr_hcall.c b/hw/ppc/spapr_hcall.c
>> index 12f8c33..58103ef 100644
>> --- a/hw/ppc/spapr_hcall.c
>> +++ b/hw/ppc/spapr_hcall.c
>> @@ -332,6 +332,15 @@ static target_ulong h_read(PowerPCCPU *cpu, sPAPRMachineState *spapr,
>> return H_SUCCESS;
>> }
>>
>> +static target_ulong h_set_sprg0(PowerPCCPU *cpu, sPAPRMachineState *spapr,
>> + target_ulong opcode, target_ulong *args)
>> +{
>> + CPUState *cs = CPU(cpu);
>> +
>> + set_spr(cs, SPR_SPRG0, args[0], -1L);
>
> This looks correct, but I think set_spr() is serious overkill here.
> It does some fancy synchronization designed for setting one cpu's SPR
> from an hcall executed on a different CPU. In this case the calling
> CPU is just setting its own SPRG0, so just
> cpu_synchronize_state()
> env->spr[SPR_SPRG0] = XXX
>
> Should be sufficient.
AFAIK the synchronization stuff is skipped when set_spr() runs already
on the destination CPU, but ok, since h-calls should be fast, I can
change this anyway to save some precious cycles.
Thomas
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next prev parent reply other threads:[~2016-02-11 7:13 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-02-10 18:09 [Qemu-devel] [PATCH 0/4] hw/ppc/spapr: Add "Processor Register Hypervisor Resource Access" H-calls Thomas Huth
2016-02-10 18:09 ` [Qemu-devel] [PATCH 1/4] hw/ppc/spapr: Add h_set_sprg0 hypercall Thomas Huth
2016-02-10 23:30 ` David Gibson
2016-02-11 7:12 ` Thomas Huth [this message]
2016-02-10 18:09 ` [Qemu-devel] [PATCH 2/4] hw/ppc/spapr: Implement h_set_dabr Thomas Huth
2016-02-10 23:36 ` David Gibson
2016-02-10 18:09 ` [Qemu-devel] [PATCH 3/4] hw/ppc/spapr: Implement the h_set_xdabr hypercall Thomas Huth
2016-02-10 23:37 ` David Gibson
2016-02-10 18:09 ` [Qemu-devel] [PATCH 4/4] hw/ppc/spapr: Implement the h_page_init hypercall Thomas Huth
2016-02-10 23:47 ` David Gibson
2016-02-11 7:53 ` Thomas Huth
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