Re: [PATCH v9 03/17] target/riscv: save and restore elp state on priv tr

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Re: [PATCH v9 03/17] target/riscv: save and restore elp state on priv tr

From:	Richard Henderson
Subject:	Re: [PATCH v9 03/17] target/riscv: save and restore elp state on priv transitions
Date:	Tue, 27 Aug 2024 14:29:10 +1000
User-agent:	Mozilla Thunderbird

On 8/27/24 14:03, Alistair Francis wrote:

On Tue, Aug 27, 2024 at 1:58 PM Richard Henderson
<richard.henderson@linaro.org> wrote:


On 8/27/24 13:53, Alistair Francis wrote:

Exposing the *envcfg CSRs to userspace seems tricky as everything is
currently built with the S/M CSRs removed from user builds.


It is as simple as moving them out of ifdefs, then initializing them as needed 
in reset
for CONFIG_USER_ONLY.  That's what we do for Arm.


Is that really better though?

Then we have these CSRs that are included in the build, so people can
write code that checks the CSRs, but they are never actually changed.

I guess it simplified the CONFIG_USER_ONLY checks, which is handy and
your original point. But it seems like it is clunky that we have these
CSRs that are kind of fake

They're not fake. They're a reflection of how the system-mode kernel configures thesystem-mode user environment.

The u[bf]cfien variables introduced in this patch set are an indication of this. Withinthis patch set they're always false. But the intent is to implement the (proposed) prctlsyscalls that will set them to true (on hold waiting for kernel abi to land upstream, butwere present in an earlier patch set revision.)

The correct implementation of those syscalls, in my opinion, is to set the corresponding[ms]envcfg bits. Just as linux-user/aarch64/target_prctl.h does for SVE et al.

r~

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Re: [PATCH v9 01/17] target/riscv: Add zicfilp extension, (continued)
- [PATCH v9 02/17] target/riscv: Introduce elp state and enabling controls for zicfilp, Deepak Gupta, 2024/08/26
  - Re: [PATCH v9 02/17] target/riscv: Introduce elp state and enabling controls for zicfilp, Alistair Francis, 2024/08/26
- [PATCH v9 03/17] target/riscv: save and restore elp state on priv transitions, Deepak Gupta, 2024/08/26
  - Re: [PATCH v9 03/17] target/riscv: save and restore elp state on priv transitions, Richard Henderson, 2024/08/26
    - Re: [PATCH v9 03/17] target/riscv: save and restore elp state on priv transitions, Deepak Gupta, 2024/08/26
    - Re: [PATCH v9 03/17] target/riscv: save and restore elp state on priv transitions, Richard Henderson, 2024/08/26
    - Re: [PATCH v9 03/17] target/riscv: save and restore elp state on priv transitions, Alistair Francis, 2024/08/26
    - Re: [PATCH v9 03/17] target/riscv: save and restore elp state on priv transitions, Richard Henderson, 2024/08/26
    - Re: [PATCH v9 03/17] target/riscv: save and restore elp state on priv transitions, Alistair Francis, 2024/08/27
    - Re: [PATCH v9 03/17] target/riscv: save and restore elp state on priv transitions, Richard Henderson <=
    - Re: [PATCH v9 03/17] target/riscv: save and restore elp state on priv transitions, Alistair Francis, 2024/08/27
- [PATCH v9 05/17] target/riscv: tracking indirect branches (fcfi) for zicfilp, Deepak Gupta, 2024/08/26
  - Re: [PATCH v9 05/17] target/riscv: tracking indirect branches (fcfi) for zicfilp, Alistair Francis, 2024/08/26
- [PATCH v9 04/17] target/riscv: additional code information for sw check, Deepak Gupta, 2024/08/26
  - Re: [PATCH v9 04/17] target/riscv: additional code information for sw check, Alistair Francis, 2024/08/26
- [PATCH v9 07/17] disas/riscv: enable `lpad` disassembly, Deepak Gupta, 2024/08/26
  - Re: [PATCH v9 07/17] disas/riscv: enable `lpad` disassembly, Alistair Francis, 2024/08/27
- [PATCH v9 09/17] target/riscv: introduce ssp and enabling controls for zicfiss, Deepak Gupta, 2024/08/26
- [PATCH v9 12/17] target/riscv: AMO operations always raise store/AMO fault, Deepak Gupta, 2024/08/26
  - Re: [PATCH v9 12/17] target/riscv: AMO operations always raise store/AMO fault, Richard Henderson, 2024/08/26

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