[PATCH v2 08/21] arm64: KVM: Implement debug save/restore
Marc Zyngier
marc.zyngier at arm.com
Tue Dec 1 07:01:16 PST 2015
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 at 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 at 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.
>>> 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?
Thanks,
M.
--
Jazz is not dead. It just smells funny...
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