Re: [PATCH v2 04/21] arm64: KVM: Implement vgic-v3 save/restore

[Christoffer Dall <christoffer.dall@linaro.org>]

On Tue, Dec 01, 2015 at 11:32:20AM +0000, Marc Zyngier wrote:
> On 30/11/15 19:50, Christoffer Dall wrote:
> > On Fri, Nov 27, 2015 at 06:49:58PM +0000, Marc Zyngier wrote:
> >> Implement the vgic-v3 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/hyp.h        |   3 +
> >>  arch/arm64/kvm/hyp/vgic-v3-sr.c | 222 ++++++++++++++++++++++++++++++++++++++++
> >>  3 files changed, 226 insertions(+)
> >>  create mode 100644 arch/arm64/kvm/hyp/vgic-v3-sr.c
> >>
> >> diff --git a/arch/arm64/kvm/hyp/Makefile b/arch/arm64/kvm/hyp/Makefile
> >> index d8d5968..d1e38ce 100644
> >> --- a/arch/arm64/kvm/hyp/Makefile
> >> +++ b/arch/arm64/kvm/hyp/Makefile
> >> @@ -3,3 +3,4 @@
> >>  #
> >>  
> >>  obj-$(CONFIG_KVM_ARM_HOST) += vgic-v2-sr.o
> >> +obj-$(CONFIG_KVM_ARM_HOST) += vgic-v3-sr.o
> >> diff --git a/arch/arm64/kvm/hyp/hyp.h b/arch/arm64/kvm/hyp/hyp.h
> >> index 78f25c4..a31cb6e 100644
> >> --- a/arch/arm64/kvm/hyp/hyp.h
> >> +++ b/arch/arm64/kvm/hyp/hyp.h
> >> @@ -30,5 +30,8 @@
> >>  void __vgic_v2_save_state(struct kvm_vcpu *vcpu);
> >>  void __vgic_v2_restore_state(struct kvm_vcpu *vcpu);
> >>  
> >> +void __vgic_v3_save_state(struct kvm_vcpu *vcpu);
> >> +void __vgic_v3_restore_state(struct kvm_vcpu *vcpu);
> >> +
> >>  #endif /* __ARM64_KVM_HYP_H__ */
> >>  
> >> diff --git a/arch/arm64/kvm/hyp/vgic-v3-sr.c b/arch/arm64/kvm/hyp/vgic-v3-sr.c
> >> new file mode 100644
> >> index 0000000..b490db5
> >> --- /dev/null
> >> +++ b/arch/arm64/kvm/hyp/vgic-v3-sr.c
> >> @@ -0,0 +1,222 @@
> >> +/*
> >> + * Copyright (C) 2012-2015 - 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/irqchip/arm-gic-v3.h>
> >> +#include <linux/kvm_host.h>
> >> +
> >> +#include <asm/kvm_mmu.h>
> >> +
> >> +#include "hyp.h"
> >> +
> >> +/*
> >> + * We store LRs in reverse order to let the CPU deal with streaming
> >> + * access. Use this macro to make it look saner...
> >> + */
> >> +#define LR_OFFSET(n)	(15 - n)
> >> +
> >> +#define read_gicreg(r)							\
> >> +	({								\
> >> +		u64 reg;						\
> >> +		asm volatile("mrs_s %0, " __stringify(r) : "=r" (reg));	\
> >> +		reg;							\
> >> +	})
> >> +
> >> +#define write_gicreg(v,r)						\
> >> +	do {								\
> >> +		u64 __val = (v);					\
> >> +		asm volatile("msr_s " __stringify(r) ", %0" : : "r" (__val));\
> >> +	} while (0)
> > 
> > remind me what the msr_s and mrs_s do compared to msr and mrs?
> 
> They do the same job, only for the system registers which are not in the
> original ARMv8 architecture spec, and most likely not implemented by
> old(er) compilers.
> 
> > are these the reason why we need separate macros to access the gic
> > registers compared to 'normal' sysregs?
> 
> Indeed.
> 
> >> +
> >> +/* vcpu is already in the HYP VA space */
> >> +void __hyp_text __vgic_v3_save_state(struct kvm_vcpu *vcpu)
> >> +{
> >> +	struct vgic_v3_cpu_if *cpu_if = &vcpu->arch.vgic_cpu.vgic_v3;
> >> +	u64 val;
> >> +	u32 nr_lr, nr_pri;
> >> +
> >> +	/*
> >> +	 * Make sure stores to the GIC via the memory mapped interface
> >> +	 * are now visible to the system register interface.
> >> +	 */
> >> +	dsb(st);
> >> +
> >> +	cpu_if->vgic_vmcr  = read_gicreg(ICH_VMCR_EL2);
> >> +	cpu_if->vgic_misr  = read_gicreg(ICH_MISR_EL2);
> >> +	cpu_if->vgic_eisr  = read_gicreg(ICH_EISR_EL2);
> >> +	cpu_if->vgic_elrsr = read_gicreg(ICH_ELSR_EL2);
> >> +
> >> +	write_gicreg(0, ICH_HCR_EL2);
> >> +	val = read_gicreg(ICH_VTR_EL2);
> >> +	nr_lr = val & 0xf;
> > 
> > this is not technically nr_lr, it's max_lr or max_lr_idx or something
> > like that.
> 
> Let's go for max_lr_idx  then.
> 
> >> +	nr_pri = ((u32)val >> 29) + 1;
> > 
> > nit: nr_pri_bits
> > 
> >> +
> >> +	switch (nr_lr) {
> >> +	case 15:
> >> +		cpu_if->vgic_lr[LR_OFFSET(15)] = read_gicreg(ICH_LR15_EL2);
> >> +	case 14:
> >> +		cpu_if->vgic_lr[LR_OFFSET(14)] = read_gicreg(ICH_LR14_EL2);
> >> +	case 13:
> >> +		cpu_if->vgic_lr[LR_OFFSET(13)] = read_gicreg(ICH_LR13_EL2);
> >> +	case 12:
> >> +		cpu_if->vgic_lr[LR_OFFSET(12)] = read_gicreg(ICH_LR12_EL2);
> >> +	case 11:
> >> +		cpu_if->vgic_lr[LR_OFFSET(11)] = read_gicreg(ICH_LR11_EL2);
> >> +	case 10:
> >> +		cpu_if->vgic_lr[LR_OFFSET(10)] = read_gicreg(ICH_LR10_EL2);
> >> +	case 9:
> >> +		cpu_if->vgic_lr[LR_OFFSET(9)] = read_gicreg(ICH_LR9_EL2);
> >> +	case 8:
> >> +		cpu_if->vgic_lr[LR_OFFSET(8)] = read_gicreg(ICH_LR8_EL2);
> >> +	case 7:
> >> +		cpu_if->vgic_lr[LR_OFFSET(7)] = read_gicreg(ICH_LR7_EL2);
> >> +	case 6:
> >> +		cpu_if->vgic_lr[LR_OFFSET(6)] = read_gicreg(ICH_LR6_EL2);
> >> +	case 5:
> >> +		cpu_if->vgic_lr[LR_OFFSET(5)] = read_gicreg(ICH_LR5_EL2);
> >> +	case 4:
> >> +		cpu_if->vgic_lr[LR_OFFSET(4)] = read_gicreg(ICH_LR4_EL2);
> >> +	case 3:
> >> +		cpu_if->vgic_lr[LR_OFFSET(3)] = read_gicreg(ICH_LR3_EL2);
> >> +	case 2:
> >> +		cpu_if->vgic_lr[LR_OFFSET(2)] = read_gicreg(ICH_LR2_EL2);
> >> +	case 1:
> >> +		cpu_if->vgic_lr[LR_OFFSET(1)] = read_gicreg(ICH_LR1_EL2);
> >> +	case 0:
> >> +		cpu_if->vgic_lr[LR_OFFSET(0)] = read_gicreg(ICH_LR0_EL2);
> > 
> > I don't understand this; LR_OFFSET(0) == (15 - 0) == 15, so
> > 
> > cpu_if->vgic_lr[15] = read_gicreg(ICH_LR0_EL2) ?
> 
> Just like in the assembly version. We store the LRs in the order we read
> them so that we don't confuse the CPU by writing backward (believe it or
> not, CPUs do get horribly confused if you do that).

but aren't we storing the wrong register to the wrong index in the
array?

Do we really access cpu_if->vgic_lr[15..12] in the C-code if the system
only has 4 LRs?

-Christoffer