[PATCH 13/20] ARM: KVM: Implement HVC_RESET_VECTORS stub hypercall

[Ard Biesheuvel]

On 17 February 2017 at 15:44, Marc Zyngier <marc.zyngier at arm.com> wrote:
> In order to restore HYP mode to its original condition, KVM currently
> implements __kvm_hyp_reset(). As we're moving towards a hyp-stub
> defined API, it becomes necessary to implement HVC_RESET_VECTORS.
>
> This patch adds the HVC_RESET_VECTORS hypercall to the KVM init
> code, which so far lacked any form of hypercall support.
>
> Signed-off-by: Marc Zyngier <marc.zyngier at arm.com>
> ---
>  arch/arm/kernel/hyp-stub.S |  1 +
>  arch/arm/kvm/init.S        | 37 +++++++++++++++++++++++++++++++------
>  2 files changed, 32 insertions(+), 6 deletions(-)
>
> diff --git a/arch/arm/kernel/hyp-stub.S b/arch/arm/kernel/hyp-stub.S
> index cf6d801f89e8..171a09cdf6b3 100644
> --- a/arch/arm/kernel/hyp-stub.S
> +++ b/arch/arm/kernel/hyp-stub.S
> @@ -280,6 +280,7 @@ ENDPROC(__hyp_reset_vectors)
>
>  .align 5
>  __hyp_stub_vectors:
> +.global __hyp_stub_vectors
>  __hyp_stub_reset:      W(b)    .
>  __hyp_stub_und:                W(b)    .
>  __hyp_stub_svc:                W(b)    .
> diff --git a/arch/arm/kvm/init.S b/arch/arm/kvm/init.S
> index bf89c919efc1..b0138118fac4 100644
> --- a/arch/arm/kvm/init.S
> +++ b/arch/arm/kvm/init.S
> @@ -23,6 +23,7 @@
>  #include <asm/kvm_asm.h>
>  #include <asm/kvm_arm.h>
>  #include <asm/kvm_mmu.h>
> +#include <asm/virt.h>
>
>  /********************************************************************
>   * Hypervisor initialization
> @@ -39,6 +40,10 @@
>   * - Setup the page tables
>   * - Enable the MMU
>   * - Profit! (or eret, if you only care about the code).
> + *
> + * Another possibility is to get a HYP stub hypercall.
> + * We discriminate between the two by checking if r0 contains a value
> + * that is less than HVC_STUB_HCALL_NR.
>   */
>
>         .text
> @@ -58,6 +63,10 @@ __kvm_hyp_init:
>         W(b)    .
>
>  __do_hyp_init:
> +       @ Check for a stub hypercall
> +       cmp     r0, #HVC_STUB_HCALL_NR
> +       blo     __kvm_handle_stub_hvc
> +
>         @ Set stack pointer
>         mov     sp, r0
>
> @@ -112,22 +121,38 @@ __do_hyp_init:
>
>         eret
>
> -       @ r0 : stub vectors address
> +ENTRY(__kvm_handle_stub_hvc)
> +       cmp     r0, #HVC_RESET_VECTORS
> +       bne     1f
>  ENTRY(__kvm_hyp_reset)
>         /* We're now in idmap, disable MMU */
>         mrc     p15, 4, r1, c1, c0, 0   @ HSCTLR
> -       ldr     r2, =(HSCTLR_M | HSCTLR_A | HSCTLR_C | HSCTLR_I)
> -       bic     r1, r1, r2
> +       ldr     r0, =(HSCTLR_M | HSCTLR_A | HSCTLR_C | HSCTLR_I)
> +       bic     r1, r1, r0
>         mcr     p15, 4, r1, c1, c0, 0   @ HSCTLR
>
> -       /* Install stub vectors */
> -       mcr     p15, 4, r0, c12, c0, 0  @ HVBAR
> -       isb
> +       /*
> +        * Install stub vectors. We cannot use 'adr' to get to the
> +        * stub vectors, hence having to play the VA->PA game.
> +        */
> +       adr     r0, .L__va2pa   @ PA
> +       ldr     r1, [r0]        @ VA
> +       sub     r0, r0, r1      @ PA - VA
> +       ldr     r1, =__hyp_stub_vectors

Since we're guaranteed to be on v7, how about something like
0:adr r0, 0b
  movw r1, #:lower16:__hyp_stub_vectors - 0b
  movt r1, #:upper16:__hyp_stub_vectors - 0b

> +       add     r1, r1, r0
> +       mcr     p15, 4, r1, c12, c0, 0  @ HVBAR
> +       b       exit
> +
> +1:     mov     r0, #-1
>
> +exit:
>         eret
> +ENDPROC(__kvm_handle_stub_hvc)
>  ENDPROC(__kvm_hyp_reset)
>
>         .ltorg
> +.L__va2pa:
> +       .word   .
>
>         .globl __kvm_hyp_init_end
>  __kvm_hyp_init_end:
> --
> 2.11.0
>
>
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