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

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Date:   Mon, 11 Jan 2021 13:53:18 +0000
From:   Marc Zyngier <maz@...nel.org>
To:     linux-arm-kernel@...ts.infradead.org, kvmarm@...ts.cs.columbia.edu,
        linux-kernel@...r.kernel.org
Cc:     Mark Rutland <mark.rutland@....com>,
        Jing Zhang <jingzhangos@...gle.com>,
        Prasad Sodagudi <psodagud@...eaurora.org>,
        Srinivas Ramana <sramana@...eaurora.org>,
        Suzuki K Poulose <suzuki.poulose@....com>,
        Catalin Marinas <catalin.marinas@....com>,
        Alexandru Elisei <alexandru.elisei@....com>,
        James Morse <james.morse@....com>,
        Ajay Patil <pajay@....qualcomm.com>, kernel-team@...roid.com,
        David Brazdil <dbrazdil@...gle.com>,
        Will Deacon <will@...nel.org>,
        Ard Biesheuvel <ardb@...nel.org>,
        Julien Thierry <julien.thierry.kdev@...il.com>
Subject: Re: [PATCH v3 04/21] arm64: Provide an 'upgrade to VHE' stub
 hypercall

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@...nel.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...