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

From: [email-masked] (Christoffer Dall)
Date: Tue, 1 Dec 2015 15:56:54 +0100

On Tue, Dec 01, 2015 at 03:47:37PM +0100, 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 <[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.
> 
Assuming I got that right:

Reviewed-by: Christoffer Dall <[email-masked]>