[PATCH v2 08/21] arm64: KVM: Implement debug save/restore

[marc.zyngier@arm.com (Marc Zyngier)]

On 01/12/15 15:41, Christoffer Dall wrote:
> On Tue, Dec 01, 2015 at 03:01:16PM +0000, Marc Zyngier wrote:
>> On 01/12/15 14:47, Christoffer Dall wrote:
>>> On Tue, Dec 01, 2015 at 01:06:31PM +0000, Marc Zyngier wrote:
>>>> On 01/12/15 12:56, Christoffer Dall wrote:
>>>>> On Fri, Nov 27, 2015 at 06:50:02PM +0000, Marc Zyngier wrote:
>>>>>> Implement the debug save restore as a direct translation of
>>>>>> the assembly code version.
>>>>>>
>>>>>> Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
>>>>>> ---
>>>>>>  arch/arm64/kvm/hyp/Makefile   |   1 +
>>>>>>  arch/arm64/kvm/hyp/debug-sr.c | 130 ++++++++++++++++++++++++++++++++++++++++++
>>>>>>  arch/arm64/kvm/hyp/hyp.h      |   9 +++
>>>>>>  3 files changed, 140 insertions(+)
>>>>>>  create mode 100644 arch/arm64/kvm/hyp/debug-sr.c
>>>>>>
>>>>>> diff --git a/arch/arm64/kvm/hyp/Makefile b/arch/arm64/kvm/hyp/Makefile
>>>>>> index ec94200..ec14cac 100644
>>>>>> --- a/arch/arm64/kvm/hyp/Makefile
>>>>>> +++ b/arch/arm64/kvm/hyp/Makefile
>>>>>> @@ -6,3 +6,4 @@ obj-$(CONFIG_KVM_ARM_HOST) += vgic-v2-sr.o
>>>>>>  obj-$(CONFIG_KVM_ARM_HOST) += vgic-v3-sr.o
>>>>>>  obj-$(CONFIG_KVM_ARM_HOST) += timer-sr.o
>>>>>>  obj-$(CONFIG_KVM_ARM_HOST) += sysreg-sr.o
>>>>>> +obj-$(CONFIG_KVM_ARM_HOST) += debug-sr.o
>>>>>> diff --git a/arch/arm64/kvm/hyp/debug-sr.c b/arch/arm64/kvm/hyp/debug-sr.c
>>>>>> new file mode 100644
>>>>>> index 0000000..a0b2b99
>>>>>> --- /dev/null
>>>>>> +++ b/arch/arm64/kvm/hyp/debug-sr.c
>>>>>> @@ -0,0 +1,130 @@
>>>>>> +/*
>>>>>> + * Copyright (C) 2015 - ARM Ltd
>>>>>> + * Author: Marc Zyngier <marc.zyngier@arm.com>
>>>>>> + *
>>>>>> + * 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/compiler.h>
>>>>>> +#include <linux/kvm_host.h>
>>>>>> +
>>>>>> +#include <asm/kvm_mmu.h>
>>>>>> +
>>>>>> +#include "hyp.h"
>>>>>> +
>>>>>> +#define read_debug(r,n)		read_sysreg(r##n##_el1)
>>>>>> +#define write_debug(v,r,n)	write_sysreg(v, r##n##_el1)
>>>>>> +
>>>>>> +#define save_debug(ptr,reg,nr)						\
>>>>>> +	switch (nr) {							\
>>>>>> +	case 15:	ptr[15] = read_debug(reg, 15);			\
>>>>>> +	case 14:	ptr[14] = read_debug(reg, 14);			\
>>>>>> +	case 13:	ptr[13] = read_debug(reg, 13);			\
>>>>>> +	case 12:	ptr[12] = read_debug(reg, 12);			\
>>>>>> +	case 11:	ptr[11] = read_debug(reg, 11);			\
>>>>>> +	case 10:	ptr[10] = read_debug(reg, 10);			\
>>>>>> +	case 9:		ptr[9] = read_debug(reg, 9);			\
>>>>>> +	case 8:		ptr[8] = read_debug(reg, 8);			\
>>>>>> +	case 7:		ptr[7] = read_debug(reg, 7);			\
>>>>>> +	case 6:		ptr[6] = read_debug(reg, 6);			\
>>>>>> +	case 5:		ptr[5] = read_debug(reg, 5);			\
>>>>>> +	case 4:		ptr[4] = read_debug(reg, 4);			\
>>>>>> +	case 3:		ptr[3] = read_debug(reg, 3);			\
>>>>>> +	case 2:		ptr[2] = read_debug(reg, 2);			\
>>>>>> +	case 1:		ptr[1] = read_debug(reg, 1);			\
>>>>>> +	default:	ptr[0] = read_debug(reg, 0);			\
>>>>>> +	}
>>>>>> +
>>>>>> +#define restore_debug(ptr,reg,nr)					\
>>>>>> +	switch (nr) {							\
>>>>>> +	case 15:	write_debug(ptr[15], reg, 15);			\
>>>>>> +	case 14:	write_debug(ptr[14], reg, 14);			\
>>>>>> +	case 13:	write_debug(ptr[13], reg, 13);			\
>>>>>> +	case 12:	write_debug(ptr[12], reg, 12);			\
>>>>>> +	case 11:	write_debug(ptr[11], reg, 11);			\
>>>>>> +	case 10:	write_debug(ptr[10], reg, 10);			\
>>>>>> +	case 9:		write_debug(ptr[9], reg, 9);			\
>>>>>> +	case 8:		write_debug(ptr[8], reg, 8);			\
>>>>>> +	case 7:		write_debug(ptr[7], reg, 7);			\
>>>>>> +	case 6:		write_debug(ptr[6], reg, 6);			\
>>>>>> +	case 5:		write_debug(ptr[5], reg, 5);			\
>>>>>> +	case 4:		write_debug(ptr[4], reg, 4);			\
>>>>>> +	case 3:		write_debug(ptr[3], reg, 3);			\
>>>>>> +	case 2:		write_debug(ptr[2], reg, 2);			\
>>>>>> +	case 1:		write_debug(ptr[1], reg, 1);			\
>>>>>> +	default:	write_debug(ptr[0], reg, 0);			\
>>>>>> +	}
>>>>>> +
>>>>>> +void __hyp_text __debug_save_state(struct kvm_vcpu *vcpu,
>>>>>> +				   struct kvm_guest_debug_arch *dbg,
>>>>>> +				   struct kvm_cpu_context *ctxt)
>>>>>> +{
>>>>>> +	if (vcpu->arch.debug_flags & KVM_ARM64_DEBUG_DIRTY) {
>>>>>> +		u64 aa64dfr0 = read_sysreg(id_aa64dfr0_el1);
>>>>>> +		int brps, wrps;
>>>>>> +
>>>>>> +		brps = (aa64dfr0 >> 12) & 0xf;
>>>>>> +		wrps = (aa64dfr0 >> 20) & 0xf;
>>>>>> +
>>>>>> +		save_debug(dbg->dbg_bcr, dbgbcr, brps);
>>>>>> +		save_debug(dbg->dbg_bvr, dbgbvr, brps);
>>>>>> +		save_debug(dbg->dbg_wcr, dbgwcr, wrps);
>>>>>> +		save_debug(dbg->dbg_wvr, dbgwvr, wrps);
>>>>>> +
>>>>>> +		ctxt->sys_regs[MDCCINT_EL1] = read_sysreg(mdccint_el1);
>>>>>> +	}
>>>>>> +}
>>>>>> +
>>>>>> +void __hyp_text __debug_restore_state(struct kvm_vcpu *vcpu,
>>>>>> +				      struct kvm_guest_debug_arch *dbg,
>>>>>> +				      struct kvm_cpu_context *ctxt)
>>>>>> +{
>>>>>> +	if (vcpu->arch.debug_flags & KVM_ARM64_DEBUG_DIRTY) {
>>>>>> +		u64 aa64dfr0 = read_sysreg(id_aa64dfr0_el1);
>>>>>> +		int brps, wrps;
>>>>>> +
>>>>>> +		brps = (aa64dfr0 >> 12) & 0xf;
>>>>>> +		wrps = (aa64dfr0 >> 20) & 0xf;
>>>>>> +
>>>>>> +		restore_debug(dbg->dbg_bcr, dbgbcr, brps);
>>>>>> +		restore_debug(dbg->dbg_bvr, dbgbvr, brps);
>>>>>> +		restore_debug(dbg->dbg_wcr, dbgwcr, wrps);
>>>>>> +		restore_debug(dbg->dbg_wvr, dbgwvr, wrps);
>>>>>> +
>>>>>> +		write_sysreg(ctxt->sys_regs[MDCCINT_EL1], mdccint_el1);
>>>>>> +	}
>>>>>> +}
>>>>>> +
>>>>>> +void __hyp_text __debug_cond_save_host_state(struct kvm_vcpu *vcpu)
>>>>>> +{
>>>>>> +	if ((vcpu->arch.ctxt.sys_regs[MDSCR_EL1] & DBG_MDSCR_KDE) ||
>>>>>> +	    (vcpu->arch.ctxt.sys_regs[MDSCR_EL1] & DBG_MDSCR_KDE))
>>>>>> +		vcpu->arch.debug_flags |= KVM_ARM64_DEBUG_DIRTY;
>>>>>> +
>>>>>> +	__debug_save_state(vcpu, &vcpu->arch.host_debug_state,
>>>>>> +			   kern_hyp_va(vcpu->arch.host_cpu_context));
>>>>>
>>>>> doesn't the assmebly code jump across saving this state neither bits are
>>>>> set where this always saves the state?
>>>>
>>>> It doesn't. The save/restore functions are guarded by tests on
>>>> KVM_ARM64_DEBUG_DIRTY, just like we have skip_debug_state on all actions
>>>> involving the save/restore in the assembly version.
>>>
>>> I think the confusing part is that the save function unconditionally
>>> calls __debug_save_state where the restore function only calls it when
>>> the dirty flag is set.  Plus I suck at reading assembly apparently.
>>
>> So the way I initially wrote it, I had the same 'if' statement as in the
>> restore function, making them fairly symmetric. But it quickly became
>> obvious that this double-if was a bit pointless.
>>
>> And actually, I wonder if I shouldn't drop it from the restore function,
>> because it only save us a spurious clear of the dirty bit.
>>
> 
> I would just move the __debug_restore_state call above the conditional,
> then they look more symmetric.  Does that work?
> 
>>>>> in any case, I feel some context is lost when this is moved away from
>>>>> assembly and understanding this patch would be easier if the semantics
>>>>> of these two _cond functions were documented.
>>>>
>>>> I can migrate the existing comments if you think that helps.
>>>>
>>> It just wasn't not quite clear to me exactly when
>>> __debug_cond_save_host_state is called for example - is this going to be
>>> called unconditionally on every entry - that's how I understand it now
>>> anyway.
>>
>> On every entry, yes. I'm trying to have the guest_run function as simple
>> as possible, with the various subsystems making their 'own' decisions.
>>
>> Not optimal (you get to branch for nothing), but clearer. At least for
>> me, but I may be the odd duck out here. Any idea to make the flow look
>> clearer?
>>
> 
> For me, if you always make the call unconditionally on both paths and
> then change the implementations to do 
> 
> 	if (!(vcpu->arch.debug_flags & KVM_ARM64_DEBUG_DIRTY))
> 		return;
> 
> then I think it's clear enough.

Fair enough. I'll rework it that way.

Thanks,

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