Re: [PATCH v3 04/21] arm64: Provide an 'upgrade to VHE' stub hypercall

Marc Zyngier
2021-01-11T13:54:16Z

On 2021-01-11 13:27, Marc Zyngier 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.

Famous last words...

>
> Signed-off-by: Marc Zyngier <maz@kernel.org>
> ---
> arch/arm64/include/asm/virt.h | 7 +++-
> arch/arm64/kernel/hyp-stub.S | 67 +++++++++++++++++++++++++++++++++--
> 2 files changed, 71 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..0a84602344eb 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 +47,13 @@ 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 mutate_to_vhe

And of course, I managed to send the *wrong* version of this patch.
This should obviously be a "b.eq", otherwise none of the other
hypercalls are reachable...

The correct version of this is now pushed in my tree[1].

Thanks,

M.

[1]
https://git.kernel.org/pub/scm/linux/kernel/git/maz/arm-platforms.git/log/?h=hack/arm64-early-cpufeature
--
Jazz is not dead. It just smells funny...