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From: Peter Maydell <peter.maydell@linaro.org>
Date: Sat, 14 May 2016 11:08:28 +0100
Message-ID: <CAFEAcA-sc7-yoLCb5sh-1jN4er7aMcQgM9kWed5--90_cqXmiQ@mail.gmail.com>
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Subject: Re: [Qemu-devel] [PATCH] target-arm/helper.c: fix access rights of
 SP_ELs
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To: Tsung-Han Lin <tsunghan.tw@gmail.com>
Cc: qemu-arm <qemu-arm@nongnu.org>, QEMU Developers <qemu-devel@nongnu.org>

On 14 May 2016 at 06:07, Tsung-Han Lin <tsunghan.tw@gmail.com> wrote:
> Fix the access rights of SP_EL2 and SP_EL1, which should be able to be
> accessed from EL2 and EL1 respectively.
>
> Signed-off-by: Tsung-Han Lin <tsunghan.tw@gmail.com>
> ---
>  target-arm/helper.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/target-arm/helper.c b/target-arm/helper.c
> index a2ab701ca5c2..8d4b03b5141b 100644
> --- a/target-arm/helper.c
> +++ b/target-arm/helper.c
> @@ -3326,7 +3326,7 @@ static const ARMCPRegInfo v8_cp_reginfo[] = {
>        .fieldoffset = offsetof(CPUARMState, sp_el[0]) },
>      { .name = "SP_EL1", .state = ARM_CP_STATE_AA64,
>        .opc0 = 3, .opc1 = 4, .crn = 4, .crm = 1, .opc2 = 0,
> -      .access = PL2_RW, .type = ARM_CP_ALIAS,
> +      .access = PL1_RW, .type = ARM_CP_ALIAS,
>        .fieldoffset = offsetof(CPUARMState, sp_el[1]) },
>      { .name = "SPSel", .state = ARM_CP_STATE_AA64,
>        .opc0 = 3, .opc1 = 0, .crn = 4, .crm = 2, .opc2 = 0,
> @@ -3526,7 +3526,7 @@ static const ARMCPRegInfo el2_cp_reginfo[] = {
>        .resetvalue = 0 },
>      { .name = "SP_EL2", .state = ARM_CP_STATE_AA64,
>        .opc0 = 3, .opc1 = 6, .crn = 4, .crm = 1, .opc2 = 0,
> -      .access = PL3_RW, .type = ARM_CP_ALIAS,
> +      .access = PL2_RW, .type = ARM_CP_ALIAS,
>        .fieldoffset = offsetof(CPUARMState, sp_el[2]) },
>      { .name = "CPTR_EL2", .state = ARM_CP_STATE_BOTH,
>        .opc0 = 3, .opc1 = 4, .crn = 1, .crm = 1, .opc2 = 2,

The ARM ARM defines that SP_EL1 is accessible only from
EL2 or higher via the system-register instructions, and
SP_EL2 only from EL3 or higher (see table C5-7 on page
C5-288 of the v8 ARM ARM DDI0487A.h, or the register description
pages for the two registers). Why do you think this is a correct
change?

thanks
-- PMM