linux-kernel - Re: [PATCH] riscv: Move user-visible sbi ext ids to uapi

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Message-Id: <fe1f3a3e-a6e2-4d4d-b7da-0f4689bda34a@lanxincomputing.com>
Date: Thu, 25 Sep 2025 10:09:48 +0800
From: "BillXiang" <xiangwencheng@...xincomputing.com>
To: "Andrew Jones" <ajones@...tanamicro.com>
Cc: <anup@...infault.org>, <kvm-riscv@...ts.infradead.org>, 
	<linux-kernel@...r.kernel.org>, <paul.walmsley@...ive.com>, 
	<palmer@...belt.com>, <aou@...s.berkeley.edu>, <alex@...ti.fr>, 
	<atishp@...osinc.com>
Subject: Re: [PATCH] riscv: Move user-visible sbi ext ids to uapi

On 9/24/2025 8:54 PM, Andrew Jones wrote:
> On Wed, Sep 24, 2025 at 10:35:25AM +0800, BillXiang wrote:
>> On 9/24/2025 4:14 AM, Andrew Jones wrote:
>>> On Wed, Sep 17, 2025 at 04:52:46PM +0800, BillXiang wrote:
>>>> Move those sbi ext ids to uapi because they will be forwarded
>>>> to user space by kvm.
>>>
>>> We don't need to publish the IDs in UAPI since they are already known to
>>> userspace by reading the SBI spec. Indeed QEMU already defines all of
>>> these except for the experimental range.>
>>> What problem are you trying to solve?
>>
>>
>> I'm working on rust-vmm[1], which auto-generates the ID constants
>> from uapi/kvm.h via bindgen[2]. Any ID that isn't exported there is
>> invisible to us. I expect other VMMs besides QEMU will need these
>> numbers as well, so let's keep one canonical definition in the UAPI
>> headers for everyone to share.
> 
> But KVM isn't the authority on these IDs, the spec is. KVM and its
> userspaces are just some implementations of SBI. M-mode software
> and other hypervisors also implements SBI.
> 
> For Rust you can use https://docs.rs/sbi-spec/latest/sbi_spec/ to get
> the constants you're looking for.

This is a good idea. I'll try it.

Thanks,
bill

> 
> Thanks,
> drew
> 
>>
>>
>> [1] https://github.com/rust-vmm
>> [2] https://crates.io/crates/bindgen
>>
>>>
>>> Thanks,
>>> drew
>>>
>>>>
>>>> Signed-off-by: BillXiang <xiangwencheng@...xincomputing.com>
>>>> ---
>>>>    arch/riscv/include/asm/sbi.h      | 16 +-----------
>>>>    arch/riscv/include/uapi/asm/sbi.h | 43 +++++++++++++++++++++++++++++++
>>>>    2 files changed, 44 insertions(+), 15 deletions(-)
>>>>    create mode 100644 arch/riscv/include/uapi/asm/sbi.h
>>>>
>>>> diff --git a/arch/riscv/include/asm/sbi.h b/arch/riscv/include/asm/sbi.h
>>>> index 341e74238aa0..e196feaabb2e 100644
>>>> --- a/arch/riscv/include/asm/sbi.h
>>>> +++ b/arch/riscv/include/asm/sbi.h
>>>> @@ -10,13 +10,12 @@
>>>>    #include <linux/types.h>
>>>>    #include <linux/cpumask.h>
>>>>    #include <linux/jump_label.h>
>>>> +#include <uapi/asm/sbi.h>
>>>>    
>>>>    #ifdef CONFIG_RISCV_SBI
>>>>    enum sbi_ext_id {
>>>>    #ifdef CONFIG_RISCV_SBI_V01
>>>>    	SBI_EXT_0_1_SET_TIMER = 0x0,
>>>> -	SBI_EXT_0_1_CONSOLE_PUTCHAR = 0x1,
>>>> -	SBI_EXT_0_1_CONSOLE_GETCHAR = 0x2,
>>>>    	SBI_EXT_0_1_CLEAR_IPI = 0x3,
>>>>    	SBI_EXT_0_1_SEND_IPI = 0x4,
>>>>    	SBI_EXT_0_1_REMOTE_FENCE_I = 0x5,
>>>> @@ -37,13 +36,6 @@ enum sbi_ext_id {
>>>>    	SBI_EXT_NACL = 0x4E41434C,
>>>>    	SBI_EXT_FWFT = 0x46574654,
>>>>    
>>>> -	/* Experimentals extensions must lie within this range */
>>>> -	SBI_EXT_EXPERIMENTAL_START = 0x08000000,
>>>> -	SBI_EXT_EXPERIMENTAL_END = 0x08FFFFFF,
>>>> -
>>>> -	/* Vendor extensions must lie within this range */
>>>> -	SBI_EXT_VENDOR_START = 0x09000000,
>>>> -	SBI_EXT_VENDOR_END = 0x09FFFFFF,
>>>>    };
>>>>    
>>>>    enum sbi_ext_base_fid {
>>>> @@ -263,12 +255,6 @@ enum sbi_pmu_ctr_type {
>>>>    #define SBI_PMU_STOP_FLAG_RESET BIT(0)
>>>>    #define SBI_PMU_STOP_FLAG_TAKE_SNAPSHOT BIT(1)
>>>>    
>>>> -enum sbi_ext_dbcn_fid {
>>>> -	SBI_EXT_DBCN_CONSOLE_WRITE = 0,
>>>> -	SBI_EXT_DBCN_CONSOLE_READ = 1,
>>>> -	SBI_EXT_DBCN_CONSOLE_WRITE_BYTE = 2,
>>>> -};
>>>> -
>>>>    /* SBI STA (steal-time accounting) extension */
>>>>    enum sbi_ext_sta_fid {
>>>>    	SBI_EXT_STA_STEAL_TIME_SET_SHMEM = 0,
>>>> diff --git a/arch/riscv/include/uapi/asm/sbi.h b/arch/riscv/include/uapi/asm/sbi.h
>>>> new file mode 100644
>>>> index 000000000000..d29ac0abeefe
>>>> --- /dev/null
>>>> +++ b/arch/riscv/include/uapi/asm/sbi.h
>>>> @@ -0,0 +1,43 @@
>>>> +/* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */
>>>> +/*
>>>> + * Copyright (C) 2025 Lanxincomputing Corporation or its affiliates.
>>>> + *
>>>> + * Authors:
>>>> + *     BillXiang <xiangwencheng@...xincomputing.com>
>>>> + */
>>>> +
>>>> +#ifndef _UAPI_ASM_RISCV_SBI_H
>>>> +#define _UAPI_ASM_RISCV_SBI_H
>>>> +
>>>> +
>>>> +enum SBI_EXT_ID {
>>>> +	/*
>>>> +	* The CONSOLE_GETCHAR/CONSOLE_PUTCHAR SBI calls cannot be
>>>> +	* handled in kernel so they will be forwarded to userspace by kvm.
>>>> +	*/
>>>> +	SBI_EXT_0_1_CONSOLE_PUTCHAR = 0x1,
>>>> +	SBI_EXT_0_1_CONSOLE_GETCHAR = 0x2,
>>>> +	/*
>>>> +	* Both SBI experimental and vendor extensions are
>>>> +	* unconditionally forwarded to userspace by kvm.
>>>> +	*/
>>>> +	/* Experimentals extensions must lie within this range */
>>>> +	SBI_EXT_EXPERIMENTAL_START = 0x08000000,
>>>> +	SBI_EXT_EXPERIMENTAL_END = 0x08FFFFFF,
>>>> +
>>>> +	/* Vendor extensions must lie within this range */
>>>> +	SBI_EXT_VENDOR_START = 0x09000000,
>>>> +	SBI_EXT_VENDOR_END = 0x09FFFFFF,
>>>> +};
>>>> +
>>>> +/*
>>>> +* The SBI debug console functions are unconditionally
>>>> +* forwarded to the userspace by kvm.
>>>> +*/
>>>> +enum sbi_ext_dbcn_fid {
>>>> +	SBI_EXT_DBCN_CONSOLE_WRITE = 0,
>>>> +	SBI_EXT_DBCN_CONSOLE_READ = 1,
>>>> +	SBI_EXT_DBCN_CONSOLE_WRITE_BYTE = 2,
>>>> +};
>>>> +
>>>> +#endif /* _UAPI_ASM_RISCV_SBI_H */
>>>> \ No newline at end of file
>>>> -- 
>>>> 2.43.0