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

From: [email-masked] (Christoffer Dall)
Date: Tue, 1 Dec 2015 15:47:37 +0100

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 <[email-masked]>
> >> ---
> >>  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 <[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/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.

> 
> > 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.

Thanks,
-Christoffer