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From: Gustavo Romero <gustavo.romero@linaro.org>
To: qemu-devel@nongnu.org
Subject: Re: [RFC PATCH 0/4] No-op support for Arm FEAT_XS, feedback needed
Date: Mon, 14 Oct 2024 14:32:35 -0300	[thread overview]
Message-ID: <b274d731-36ed-454b-9ad6-c58c6443d520@linaro.org> (raw)
In-Reply-To: <20241014-arm-feat-xs-v1-0-42bb714d6b11@linaro.org>

Hi Manos,

On 10/14/24 07:48, Manos Pitsidianakis wrote:
> This series is an initial incomplete attempt at adding support for the
> FEAT_XS feature in aarch64 TCG. This feature was introduced in ARMv8.7:
> it adds a new memory attribute XS which indicates that a memory access
> could take longer than usual to complete and also adds instruction
> variants for TLBI maintenance and DSB.
> 
> These variants are implemented as no-ops, since QEMU TCG doesn't
> implement caching.
> 
> This is my first foray into TCG and certain things weren't clear to me:
> 
> 1. How to make sure the feature is implemented properly. Since we model
>     cache maintenance as no-ops my understanding is the only
>     functionality we need to provide is to expose the FEAT_XS feature bit
>     and also make sure the nXS variants trap properly if configured with
>     fine-grained traps.
> 2. Is there a point in adding a TCG test? If I read the manual
>     correctly, the nXS variants should trap to the undefined instruction
>     vector if unimplemented.

Yes, I think a test as the one you provided is worth to at least, as you
mentioned, check if QEMU doesn't crash when encountering NXS instruction
variants.


Cheers,
Gustavo


> These patches lack support for FGT for now.
> 
> Signed-off-by: Manos Pitsidianakis <manos.pitsidianakis@linaro.org>
> ---
> Manos Pitsidianakis (4):
>        arm: Add FEAT_XS's TLBI NXS variants
>        arm/tcg: add decodetree entry for DSB nXS variant
>        arm/tcg/cpu64: add FEAT_XS feat in max cpu
>        tests/tcg/aarch64: add system test for FEAT_XS
> 
>   target/arm/cpu-features.h          |   5 +
>   target/arm/helper.c                | 366 +++++++++++++++++++++----------------
>   target/arm/tcg/a64.decode          |   3 +
>   target/arm/tcg/cpu64.c             |   1 +
>   target/arm/tcg/translate-a64.c     |   6 +
>   tests/tcg/aarch64/system/feat-xs.c |  27 +++
>   6 files changed, 255 insertions(+), 153 deletions(-)
> ---
> base-commit: 7e3b6d8063f245d27eecce5aabe624b5785f2a77
> change-id: 20240919-arm-feat-xs-73eedb23d937
> 
> --
> γαῖα πυρί μιχθήτω
> 
> 



      parent reply	other threads:[~2024-10-14 17:33 UTC|newest]

Thread overview: 13+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2024-10-14 10:48 [RFC PATCH 0/4] No-op support for Arm FEAT_XS, feedback needed Manos Pitsidianakis
2024-10-14 10:48 ` [RFC PATCH 1/4] arm: Add FEAT_XS's TLBI NXS variants Manos Pitsidianakis
2024-10-14 16:21   ` Richard Henderson
2024-10-14 10:48 ` [RFC PATCH 2/4] arm/tcg: add decodetree entry for DSB nXS variant Manos Pitsidianakis
2024-10-14 16:30   ` Richard Henderson
2024-10-14 10:48 ` [RFC PATCH 3/4] arm/tcg/cpu64: add FEAT_XS feat in max cpu Manos Pitsidianakis
2024-10-14 16:31   ` Richard Henderson
2024-10-14 16:32   ` Richard Henderson
2024-10-14 10:48 ` [RFC PATCH 4/4] tests/tcg/aarch64: add system test for FEAT_XS Manos Pitsidianakis
2024-10-14 16:33   ` Richard Henderson
2024-10-14 17:35   ` Gustavo Romero
2024-10-14 16:41 ` [RFC PATCH 0/4] No-op support for Arm FEAT_XS, feedback needed Peter Maydell
2024-10-14 17:32 ` Gustavo Romero [this message]

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