Re: [PATCH 04/17] arm64: Provide an 'upgrade to VHE' stub hypercall

[Jing Zhang <jingzhangos@google.com>]

On Mon, Dec 28, 2020 at 4:50 AM Marc Zyngier <maz@kernel.org> wrote:
>
> As we are about to change the way a VHE system boots, let's
> provide the core helper, in the form of a stub hypercall that
> enables VHE and replicates the full EL1 context at EL2, thanks
> to EL1 and VHE-EL2 being extremely similar.
>
> On exception return, the kernel carries on at EL2. Fancy!
>
> Nothing calls this new hypercall yet, so no functional change.
>
> Signed-off-by: Marc Zyngier <maz@kernel.org>
> ---
>  arch/arm64/include/asm/virt.h |  7 +++-
>  arch/arm64/kernel/hyp-stub.S  | 70 ++++++++++++++++++++++++++++++++++-
>  2 files changed, 74 insertions(+), 3 deletions(-)
>
> diff --git a/arch/arm64/include/asm/virt.h b/arch/arm64/include/asm/virt.h
> index ee6a48df89d9..7379f35ae2c6 100644
> --- a/arch/arm64/include/asm/virt.h
> +++ b/arch/arm64/include/asm/virt.h
> @@ -35,8 +35,13 @@
>   */
>  #define HVC_RESET_VECTORS 2
>
> +/*
> + * HVC_VHE_RESTART - Upgrade the CPU from EL1 to EL2, if possible
> + */
> +#define HVC_VHE_RESTART        3
> +
>  /* Max number of HYP stub hypercalls */
> -#define HVC_STUB_HCALL_NR 3
> +#define HVC_STUB_HCALL_NR 4
>
>  /* Error returned when an invalid stub number is passed into x0 */
>  #define HVC_STUB_ERR   0xbadca11
> diff --git a/arch/arm64/kernel/hyp-stub.S b/arch/arm64/kernel/hyp-stub.S
> index 160f5881a0b7..6ffdc1f7778b 100644
> --- a/arch/arm64/kernel/hyp-stub.S
> +++ b/arch/arm64/kernel/hyp-stub.S
> @@ -8,9 +8,9 @@
>
>  #include <linux/init.h>
>  #include <linux/linkage.h>
> -#include <linux/irqchip/arm-gic-v3.h>
>
>  #include <asm/assembler.h>
> +#include <asm/el2_setup.h>
>  #include <asm/kvm_arm.h>
>  #include <asm/kvm_asm.h>
>  #include <asm/ptrace.h>
> @@ -47,10 +47,16 @@ SYM_CODE_END(__hyp_stub_vectors)
>
>  SYM_CODE_START_LOCAL(el1_sync)
>         cmp     x0, #HVC_SET_VECTORS
> -       b.ne    2f
> +       b.ne    1f
>         msr     vbar_el2, x1
>         b       9f
>
> +1:     cmp     x0, #HVC_VHE_RESTART
> +       b.ne    2f
> +       mov     x0, #HVC_SOFT_RESTART
> +       adr     x1, mutate_to_vhe
> +       // fall through...
> +
>  2:     cmp     x0, #HVC_SOFT_RESTART
>         b.ne    3f
>         mov     x0, x2
> @@ -70,6 +76,66 @@ SYM_CODE_START_LOCAL(el1_sync)
>         eret
>  SYM_CODE_END(el1_sync)
>
> +// nVHE? No way! Give me the real thing!
> +SYM_CODE_START_LOCAL(mutate_to_vhe)
> +       // Sanity check: MMU *must* be off
> +       mrs     x0, sctlr_el2
> +       tbnz    x0, #0, 1f
> +
> +       // Needs to be VHE capable, obviously
> +       mrs     x0, id_aa64mmfr1_el1
> +       ubfx    x0, x0, #ID_AA64MMFR1_VHE_SHIFT, #4
> +       cbz     x0, 1f
> +
> +       // Engage the VHE magic!
> +       mov_q   x0, HCR_HOST_VHE_FLAGS
> +       msr     hcr_el2, x0
> +       isb
> +
> +       // Doesn't do much on VHE, but still, worth a shot
> +       init_el2_state vhe
> +
> +       // Use the EL1 allocated stack, per-cpu offset
> +       mrs     x0, sp_el1
> +       mov     sp, x0
> +       mrs     x0, tpidr_el1
> +       msr     tpidr_el2, x0
> +
> +       // FP configuration, vectors
> +       mrs_s   x0, SYS_CPACR_EL12
> +       msr     cpacr_el1, x0
> +       mrs_s   x0, SYS_VBAR_EL12
> +       msr     vbar_el1, x0
> +
> +       // Transfert the MM state from EL1 to EL2

Transfert, typo?

> +       mrs_s   x0, SYS_TCR_EL12
> +       msr     tcr_el1, x0
> +       mrs_s   x0, SYS_TTBR0_EL12
> +       msr     ttbr0_el1, x0
> +       mrs_s   x0, SYS_TTBR1_EL12
> +       msr     ttbr1_el1, x0
> +       mrs_s   x0, SYS_MAIR_EL12
> +       msr     mair_el1, x0
> +       isb
> +
> +       // Invalidate TLBs before enabling the MMU
> +       tlbi    vmalle1
> +       dsb     nsh
> +
> +       // Enable the EL2 S1 MMU, as set up from EL1
> +       mrs_s   x0, SYS_SCTLR_EL12
> +       set_sctlr_el1   x0
> +
> +       // Hack the exception return to stay at EL2
> +       mrs     x0, spsr_el1
> +       and     x0, x0, #~PSR_MODE_MASK
> +       mov     x1, #PSR_MODE_EL2h
> +       orr     x0, x0, x1
> +       msr     spsr_el1, x0
> +
> +1:     eret
> +SYM_CODE_END(mutate_to_vhe)
> +
>  .macro invalid_vector  label
>  SYM_CODE_START_LOCAL(\label)
>         b \label
> --
> 2.29.2
>
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