Re: [v4 1/4] arm64: kvm: add a cpu tear-down function

From: Marc Zyngier
Date: Tue May 26 2015 - 10:14:20 EST

Hi Takahiro,

On 08/05/15 02:18, AKASHI Takahiro wrote:
> Cpu must be put back into its initial state, at least, in the
> following cases in order to shutdown the system and/or re-initialize cpus
> later on:
> 1) kexec/kdump
> 2) cpu hotplug (offline)
> 3) removing kvm as a module
>
> To address those issues in later patches, this patch adds a tear-down
> function, kvm_cpu_reset(), that disables D-cache & MMU and restore a vector
> table to the initial stub at EL2.
>
> Signed-off-by: AKASHI Takahiro <takahiro.akashi@xxxxxxxxxx>
> ---
> arch/arm/kvm/arm.c | 15 +++++++++++++++
> arch/arm/kvm/mmu.c | 5 +++++
> arch/arm64/include/asm/kvm_asm.h | 1 +
> arch/arm64/include/asm/kvm_host.h | 11 +++++++++++
> arch/arm64/include/asm/kvm_mmu.h | 7 +++++++
> arch/arm64/include/asm/virt.h | 11 +++++++++++
> arch/arm64/kvm/hyp-init.S | 32 ++++++++++++++++++++++++++++++++
> arch/arm64/kvm/hyp.S | 16 +++++++++++++---
> 8 files changed, 95 insertions(+), 3 deletions(-)
>
> diff --git a/arch/arm/kvm/arm.c b/arch/arm/kvm/arm.c
> index 07e7eb1..251ab9e 100644
> --- a/arch/arm/kvm/arm.c
> +++ b/arch/arm/kvm/arm.c
> @@ -897,6 +897,21 @@ static void cpu_init_hyp_mode(void *dummy)
> __cpu_init_hyp_mode(boot_pgd_ptr, pgd_ptr, hyp_stack_ptr, vector_ptr);
> }
>
> +static void kvm_cpu_reset(void *dummy)

It looks like you can entirely loose the "dummy" parameter. The only
reason some function have this is when they are used from an IPI call.

> +{
> + phys_addr_t boot_pgd_ptr;
> + phys_addr_t phys_idmap_start;
> +
> + if (__hyp_get_vectors() == hyp_default_vectors)
> + return;
> +
> + boot_pgd_ptr = kvm_mmu_get_boot_httbr();
> + phys_idmap_start = kvm_get_idmap_start();
> + __cpu_reset_hyp_mode(boot_pgd_ptr, phys_idmap_start,
> + hyp_default_vectors,
> + kvm_virt_to_trampoline(__kvm_hyp_reset));
> +}
> +
> static int hyp_init_cpu_notify(struct notifier_block *self,
> unsigned long action, void *cpu)
> {
> diff --git a/arch/arm/kvm/mmu.c b/arch/arm/kvm/mmu.c
> index 3e6859b..3631a37 100644
> --- a/arch/arm/kvm/mmu.c
> +++ b/arch/arm/kvm/mmu.c
> @@ -1490,6 +1490,11 @@ phys_addr_t kvm_get_idmap_vector(void)
> return hyp_idmap_vector;
> }
>
> +phys_addr_t kvm_get_idmap_start(void)
> +{
> + return hyp_idmap_start;
> +}
> +
> int kvm_mmu_init(void)
> {
> int err;
> diff --git a/arch/arm64/include/asm/kvm_asm.h b/arch/arm64/include/asm/kvm_asm.h
> index 4f7310f..f1c16e2 100644
> --- a/arch/arm64/include/asm/kvm_asm.h
> +++ b/arch/arm64/include/asm/kvm_asm.h
> @@ -118,6 +118,7 @@ struct kvm_vcpu;
>
> extern char __kvm_hyp_init[];
> extern char __kvm_hyp_init_end[];
> +extern char __kvm_hyp_reset[];
>
> extern char __kvm_hyp_vector[];
>
> diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
> index 8ac3c70..6a8da9c 100644
> --- a/arch/arm64/include/asm/kvm_host.h
> +++ b/arch/arm64/include/asm/kvm_host.h
> @@ -199,6 +199,8 @@ struct kvm_vcpu *kvm_arm_get_running_vcpu(void);
> struct kvm_vcpu * __percpu *kvm_get_running_vcpus(void);
>
> u64 kvm_call_hyp(void *hypfn, ...);
> +void kvm_call_reset(phys_addr_t boot_pgd_ptr, phys_addr_t phys_idmap_start,
> + unsigned long stub_vector_ptr, unsigned long reset_func);
> void force_vm_exit(const cpumask_t *mask);
> void kvm_mmu_wp_memory_region(struct kvm *kvm, int slot);
>
> @@ -223,6 +225,15 @@ static inline void __cpu_init_hyp_mode(phys_addr_t boot_pgd_ptr,
> hyp_stack_ptr, vector_ptr);
> }
>
> +static inline void __cpu_reset_hyp_mode(phys_addr_t boot_pgd_ptr,
> + phys_addr_t phys_idmap_start,
> + unsigned long stub_vector_ptr,
> + unsigned long reset_func)
> +{
> + kvm_call_reset(boot_pgd_ptr, phys_idmap_start, stub_vector_ptr,
> + reset_func);
> +}
> +
> struct vgic_sr_vectors {
> void *save_vgic;
> void *restore_vgic;
> diff --git a/arch/arm64/include/asm/kvm_mmu.h b/arch/arm64/include/asm/kvm_mmu.h
> index 6458b53..facfd6d 100644
> --- a/arch/arm64/include/asm/kvm_mmu.h
> +++ b/arch/arm64/include/asm/kvm_mmu.h
> @@ -96,6 +96,7 @@ void kvm_mmu_free_memory_caches(struct kvm_vcpu *vcpu);
> phys_addr_t kvm_mmu_get_httbr(void);
> phys_addr_t kvm_mmu_get_boot_httbr(void);
> phys_addr_t kvm_get_idmap_vector(void);
> +phys_addr_t kvm_get_idmap_start(void);
> int kvm_mmu_init(void);
> void kvm_clear_hyp_idmap(void);
>
> @@ -305,5 +306,11 @@ static inline void __kvm_flush_dcache_pud(pud_t pud)
> void kvm_set_way_flush(struct kvm_vcpu *vcpu);
> void kvm_toggle_cache(struct kvm_vcpu *vcpu, bool was_enabled);
>
> +extern char __hyp_idmap_text_start[];

If you're defining it here, then it worth considering removing the
similar declaration from mmu.c.

> +#define kvm_virt_to_trampoline(x) \
> + (TRAMPOLINE_VA \
> + + ((unsigned long)(x) \
> + - ((unsigned long)__hyp_idmap_text_start & PAGE_MASK)))
> +
> #endif /* __ASSEMBLY__ */
> #endif /* __ARM64_KVM_MMU_H__ */
> diff --git a/arch/arm64/include/asm/virt.h b/arch/arm64/include/asm/virt.h
> index 3070096..7fcd087 100644
> --- a/arch/arm64/include/asm/virt.h
> +++ b/arch/arm64/include/asm/virt.h
> @@ -61,6 +61,17 @@
> #define BOOT_CPU_MODE_EL1 (0xe11)
> #define BOOT_CPU_MODE_EL2 (0xe12)
>
> +/*
> + * HVC_RESET - Reset cpu in EL2 to initial state.
> + *
> + * @x0: entry address in trampoline code in va
> + * @x1: identical mapping page table in pa
> + * @x2: start address of identical mapping in pa
> + * @x3: initial stub vector in pa
> + */
> +
> +#define HVC_RESET 5
> +
> #ifndef __ASSEMBLY__
>
> /*
> diff --git a/arch/arm64/kvm/hyp-init.S b/arch/arm64/kvm/hyp-init.S
> index c319116..2614cfc 100644
> --- a/arch/arm64/kvm/hyp-init.S
> +++ b/arch/arm64/kvm/hyp-init.S
> @@ -115,6 +115,38 @@ target: /* We're now in the trampoline code, switch page tables */
> eret
> ENDPROC(__kvm_hyp_init)
>
> + /*
> + * x0: HYP boot pgd
> + * x1: HYP phys_idmap_start
> + * x2: HYP stub vectors
> + */
> +ENTRY(__kvm_hyp_reset)
> + /* We're in trampoline code in VA, switch back to boot page tables */
> + msr ttbr0_el2, x0
> + isb
> +
> + /* Invalidate the old TLBs */
> + tlbi alle2
> + dsb sy
> +
> + /* Branch into PA space */
> + adr x0, 1f
> + bfi x1, x0, #0, #PAGE_SHIFT
> + br x1
> +
> + /* We're now in idmap, disable MMU */
> +1: mrs x0, sctlr_el2
> + ldr x1, =SCTLR_EL2_FLAGS
> + bic x0, x0, x1 // Clear SCTL_M and etc
> + msr sctlr_el2, x0
> + isb
> +
> + /* Install stub vectors */
> + msr vbar_el2, x2

Instead of using a parameter, can't you just do

adr x2, __hyp_stub_vectors
msr vbar_el2, x2

? I can't imagine a case where we don't want this behaviour, and this
would slightly simplify the calling convention.

> +
> + eret
> +ENDPROC(__kvm_hyp_reset)
> +
> .ltorg
>
> .popsection
> diff --git a/arch/arm64/kvm/hyp.S b/arch/arm64/kvm/hyp.S
> index fd085ec..7c3bdee 100644
> --- a/arch/arm64/kvm/hyp.S
> +++ b/arch/arm64/kvm/hyp.S
> @@ -1136,6 +1136,11 @@ ENTRY(kvm_call_hyp)
> ret
> ENDPROC(kvm_call_hyp)
>
> +ENTRY(kvm_call_reset)
> + hvc #HVC_RESET
> + ret
> +ENDPROC(kvm_call_reset)
> +
> .macro invalid_vector label, target
> .align 2
> \label:
> @@ -1179,10 +1184,14 @@ el1_sync: // Guest trapped into EL2
> cmp x18, #HVC_GET_VECTORS
> b.ne 1f
> mrs x0, vbar_el2
> - b 2f
> + b 3f

How about renaming this to something like "do_eret" once and for all so
that we stop this dance each time someone adds a new entry point?
>
> -1: /* Default to HVC_CALL_HYP. */
> + /* jump into trampoline code */
> +1: cmp x18, #HVC_RESET
> + b.ne 2f
> + br x3 // no return

Same here. If we're always jumping to the trampoline code, why do we
have to pass it as a parameter?

>
> +2: /* Default to HVC_CALL_HYP. */
> push lr, xzr
>
> /*
> @@ -1196,7 +1205,8 @@ el1_sync: // Guest trapped into EL2
> blr lr
>
> pop lr, xzr
> -2: eret
> +
> +3: eret
>
> el1_trap:
> /*
>

Thanks,

M.
--
Jazz is not dead. It just smells funny...
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