Subject: [PATCH v3 11/32] arm64: KVM: CPU specific system registers handling

From: [email-masked] (Marc Zyngier)
Date: Wed, 24 Apr 2013 10:33:15 +0100

On 23/04/13 23:59, Christoffer Dall wrote:
> On Fri, Apr 12, 2013 at 05:04:14PM +0100, Marc Zyngier wrote:
>> On 10/04/13 18:06, Will Deacon wrote:
>>> On Mon, Apr 08, 2013 at 05:17:13PM +0100, Marc Zyngier wrote:
>>>> Add the support code for CPU specific system registers. Not much
>>>> here yet.
>>>>
>>>> Reviewed-by: Christopher Covington <[email-masked]>
>>>> Signed-off-by: Marc Zyngier <[email-masked]>
>>>> ---
>>>>  arch/arm64/kvm/sys_regs_generic_v8.c | 85 ++++++++++++++++++++++++++++++++++++
>>>>  1 file changed, 85 insertions(+)
>>>>  create mode 100644 arch/arm64/kvm/sys_regs_generic_v8.c
>>>>
>>>> diff --git a/arch/arm64/kvm/sys_regs_generic_v8.c b/arch/arm64/kvm/sys_regs_generic_v8.c
>>>> new file mode 100644
>>>> index 0000000..d4e8039
>>>> --- /dev/null
>>>> +++ b/arch/arm64/kvm/sys_regs_generic_v8.c
>>>> @@ -0,0 +1,85 @@
>>>> +/*
>>>> + * Copyright (C) 2012,2013 - ARM Ltd
>>>> + * Author: Marc Zyngier <[email-masked]>
>>>> + *
>>>> + * Based on arch/arm/kvm/coproc_a15.c:
>>>> + * Copyright (C) 2012 - Virtual Open Systems and Columbia University
>>>> + * Authors: Rusty Russell <[email-masked]>
>>>> + *          Christoffer Dall <[email-masked]>
>>>> + *
>>>> + * This program is free software; you can redistribute it and/or modify
>>>> + * it under the terms of the GNU General Public License, version 2, as
>>>> + * published by the Free Software Foundation.
>>>> + *
>>>> + * This program is distributed in the hope that it will be useful,
>>>> + * but WITHOUT ANY WARRANTY; without even the implied warranty of
>>>> + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
>>>> + * GNU General Public License for more details.
>>>> + *
>>>> + * You should have received a copy of the GNU General Public License
>>>> + * along with this program.  If not, see <http://www.gnu.org/licenses/>.
>>>> + */
>>>> +#include <linux/kvm_host.h>
>>>> +#include <asm/cputype.h>
>>>> +#include <asm/kvm_arm.h>
>>>> +#include <asm/kvm_asm.h>
>>>> +#include <asm/kvm_host.h>
>>>> +#include <asm/kvm_emulate.h>
>>>> +#include <asm/kvm_coproc.h>
>>>> +#include <linux/init.h>
>>>> +
>>>> +#include "sys_regs.h"
>>>> +
>>>> +static bool access_actlr(struct kvm_vcpu *vcpu,
>>>> +			 const struct sys_reg_params *p,
>>>> +			 const struct sys_reg_desc *r)
>>>> +{
>>>> +	if (p->is_write)
>>>> +		return ignore_write(vcpu, p);
>>>> +
>>>> +	*vcpu_reg(vcpu, p->Rt) = vcpu_sys_reg(vcpu, ACTLR_EL1);
>>>> +	return true;
>>>> +}
>>>> +
>>>> +static void reset_actlr(struct kvm_vcpu *vcpu, const struct sys_reg_desc *r)
>>>> +{
>>>> +	u64 actlr;
>>>> +
>>>> +	asm volatile("mrs %0, actlr_el1\n" : "=r" (actlr));
>>>> +	vcpu_sys_reg(vcpu, ACTLR_EL1) = actlr;
>>>> +}
>>>
>>> Do we actually need this? If so, there are likely other registers (things
>>> like the ectlr) that should be considered too.
>>
>> I'm focussing on the architected registers, and only those. ECTLR is
>> implementation dependent, and is not specified as an architected sysreg.
>>
>> As this is one of the registers that we trap (TACR set in HCR_EL2), we
>> have to emulate it. Now, maybe it is not that useful to trap it (nobody
>> uses that code path yet).
>>
> why is this even in a generic_v8 file then? Should it not be able to be
> handled generically in the sys_regs file and only when you have specific
> meanings of the register for a specific core should you add something
> like this file?

That would be a possibility. But I'd rather have a separate file that
describes targets, rather then stuffing this into sys_regs.c (which is
already too big for my taste), and have the implementation defined
registers there.

The AEMv8/Foundation being "generic" implementations of ARMv8, I'm
giving them their own target file. The A57 mention in this file is just
a temporary hack until I get to boot the stuff on a real A57.

> I think it's preferred to have something that traps and shouts than
> something that may or may not work (ie. just allowing the guest to read
> the register directly), but you guys know better than me what kind of
> things can be exposed through this register in the future.

At least for the models, this handling of ACTLR_EL1 should be correct.

Thanks,

	M.
-- 
Jazz is not dead. It just smells funny...