Subject: [PATCH v9 14/14] virt: arm: support hip04 gic

From: [email-masked] (Christoffer Dall)
Date: Tue, 20 May 2014 16:05:18 +0100

On Tue, May 20, 2014 at 10:16:22PM +0800, Haojian Zhuang wrote:
> On 20 May 2014 22:01, Christoffer Dall <[email-masked]> wrote:
> > On Tue, May 20, 2014 at 09:52:53PM +0800, Haojian Zhuang wrote:
> >> On 20 May 2014 21:44, Christoffer Dall <[email-masked]> wrote:
> >> > On Tue, May 20, 2014 at 09:10:27PM +0800, Haojian Zhuang wrote:
> >
> > [...]
> >
> >> >> diff --git a/virt/kvm/arm/vgic.c b/virt/kvm/arm/vgic.c
> >> >> index 47b2983..4c0c1e9 100644
> >> >> --- a/virt/kvm/arm/vgic.c
> >> >> +++ b/virt/kvm/arm/vgic.c
> >> >> @@ -76,6 +76,8 @@
> >> >>  #define IMPLEMENTER_ARM              0x43b
> >> >>  #define GICC_ARCH_VERSION_V2 0x2
> >> >>
> >> >> +#define vgic_nr_lr(vcpu)     (vcpu->hw_cfg & HWCFG_NR_LR_MASK)
> >> >> +
> >> >>  /* Physical address of vgic virtual cpu interface */
> >> >>  static phys_addr_t vgic_vcpu_base;
> >> >>
> >> >> @@ -97,7 +99,7 @@ static void vgic_retire_disabled_irqs(struct kvm_vcpu *vcpu);
> >> >>  static void vgic_update_state(struct kvm *kvm);
> >> >>  static void vgic_kick_vcpus(struct kvm *kvm);
> >> >>  static void vgic_dispatch_sgi(struct kvm_vcpu *vcpu, u32 reg);
> >> >> -static u32 vgic_nr_lr;
> >> >> +static u32 vgic_hw_cfg;
> >> >>
> >> >>  static unsigned int vgic_maint_irq;
> >> >>
> >> >> @@ -624,9 +626,9 @@ static void vgic_unqueue_irqs(struct kvm_vcpu *vcpu)
> >> >>       struct vgic_cpu *vgic_cpu = &vcpu->arch.vgic_cpu;
> >> >>       int vcpu_id = vcpu->vcpu_id;
> >> >>       int i, irq, source_cpu;
> >> >> -     u32 *lr;
> >> >> +     u32 *lr, nr_lr = vgic_nr_lr(vgic_cpu);
> >> >
> >> > This is static for any system post-boot, right?  Can't we set this
> >> > global variable once like we did before instead of having to define
> >> > these extra variables and do the bit manipulation all over the place?
> >> >
> >> > -Christoffer
> >>
> >> I tried to define a global gich_apr variable before. But Marc didn't agree on
> >> that. He suggested to use vgic_cpu_nr_lr to save both GICH_APR offset
> >> and nr_lr.
> >>
> >> Adding gich_apr variable should be the simpler implementation.
> >>
> > You're talking about storing this information on the vgic_cpu struct,
> > which is accessed on every world-switch patch.  There, you don't want
> > two memory accesses.
> >
> diff --git a/arch/arm/kvm/interrupts_head.S b/arch/arm/kvm/interrupts_head.S
> index 76af9302..b27e43f 100644
> --- a/arch/arm/kvm/interrupts_head.S
> +++ b/arch/arm/kvm/interrupts_head.S
> @@ -419,7 +419,9 @@ vcpu        .req    r0              @ vcpu pointer
> always in r0
>         ldr     r7, [r2, #GICH_EISR1]
>         ldr     r8, [r2, #GICH_ELRSR0]
>         ldr     r9, [r2, #GICH_ELRSR1]
> -       ldr     r10, [r2, #GICH_APR]
> +       ldr     r10, =gich_apr
> +       ldr     r10, [r10]
> +       ldr     r10, [r2, r10]
> 
>         str     r3, [r11, #VGIC_CPU_HCR]
>         str     r4, [r11, #VGIC_CPU_VMCR]
> @@ -435,7 +437,11 @@ vcpu       .req    r0              @ vcpu pointer
> always in r0
>         str     r5, [r2, #GICH_HCR]
> 
>         /* Save list registers */
> -       add     r2, r2, #GICH_LR0
> +       ldr     r10, =gich_apr
> +       ldr     r10, [r10]
> +       /* the offset between GICH_APR & GICH_LR0 is 0x10 */
> +       add     r10, r10, #0x10
> +       add     r2, r2, r10
>         add     r3, r11, #VGIC_CPU_LR
>         ldr     r4, [r11, #VGIC_CPU_NR_LR]
>  1:     ldr     r6, [r2], #4
> @@ -469,10 +475,16 @@ vcpu      .req    r0              @ vcpu pointer
> always in r0
> 
>         str     r3, [r2, #GICH_HCR]
>         str     r4, [r2, #GICH_VMCR]
> -       str     r8, [r2, #GICH_APR]
> +       ldr     r6, =gich_apr
> +       ldr     r6, [r6]
> +       str     r8, [r2, r6]
> 
>         /* Restore list registers */
> -       add     r2, r2, #GICH_LR0
> +       ldr     r6, =gich_apr
> +       ldr     r6, [r6]
> +       /* the offset between GICH_APR & GICH_LR0 is 0x10 */
> +       add     r6, r6, #0x10
> +       add     r2, r2, r6
>         add     r3, r11, #VGIC_CPU_LR
>         ldr     r4, [r11, #VGIC_CPU_NR_LR]
>  1:     ldr     r6, [r3], #4
> @@ -618,3 +630,7 @@ vcpu        .req    r0              @ vcpu pointer
> always in r0
>  .macro load_vcpu
>         mrc     p15, 4, vcpu, c13, c0, 2        @ HTPIDR
>  .endm
> +
> +       .global gich_apr
> +gich_apr:
> +       .long   GICH_APR
> 
> diff --git a/virt/kvm/arm/vgic.c b/virt/kvm/arm/vgic.c
> index 47b2983..6bf31db 100644
> --- a/virt/kvm/arm/vgic.c
> +++ b/virt/kvm/arm/vgic.c
> @@ -1470,17 +1470,30 @@ static struct notifier_block vgic_cpu_nb = {
>         .notifier_call = vgic_cpu_notify,
>  };
> 
> +static const struct of_device_id of_vgic_ids[] = {
> +       {
> +               .compatible = "arm,cortex-a15-gic",
> +               .data = (void *)GICH_APR,
> +       }, {
> +               .compatible = "hisilicon,hip04-gic",
> +               .data = (void *)HIP04_GICH_APR,
> +       }, {
> +       },
> +};
> +
>  int kvm_vgic_hyp_init(void)
>  {
>         int ret;
>         struct resource vctrl_res;
>         struct resource vcpu_res;
> +       const struct of_device_id *match;
> 
> -       vgic_node = of_find_compatible_node(NULL, NULL, "arm,cortex-a15-gic");
> +       vgic_node = of_find_matching_node_and_match(NULL, of_vgic_ids, &match);
>         if (!vgic_node) {
>                 kvm_err("error: no compatible vgic node in DT\n");
>                 return -ENODEV;
>         }
> +       gich_apr = (unsigned int)match->data;
> 
>         vgic_maint_irq = irq_of_parse_and_map(vgic_node, 0);
>         if (!vgic_maint_irq) {
> 
> It's the implementation of gich_apr in arm32.
> 
> We needn't add or change anything in struct vgic_cpu. And both the
> assembly code and the code could be much easier.
> 

But we do end up with an extra memory access from EL2 in the critical
path, and I believe Marc's concern here is that if we cross a cache
line, this might really hurt performance.

> > Here, on the other hand, you're in host kernel land, and you can do your
> > bit-shuffling once, and always access a single static variable like we
> > did before, which will simplify the C-code.
> >
> 
> No bit-shuffling in gich_apr implementation. Is it right?
> 

I would like to see us avoid allocating that extra nr_lr variable in
every function mucking with list registers in the C-file.

I would need to look at the data structure size and profile the
world-switch code to properly evaluate if it's worth packing the values
in a single field, so I'll let Marc comment on this one.

-Christoffer