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

Marc,

Thank you for your reviews:

On 05/26/2015 06:26 PM, Marc Zyngier wrote:

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@linaro.org

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.

OK. I will remove all of them.

...

+{

• 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.

Yes. I will remove them 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.

Yeah, but it will also enforces kvm to be statically linked to the kernel. (not module-capable) Is that OK?

...

• 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?

Good point. I will take it.

...

-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?

We need here a physical address of reset function. It seems easy to call kvm_virt_to_trampoline() in C code. But, yes, we can also do it in asm.

Thanks, -Takahiro AKASHI

...

+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.