linux-kernel - Re: [PATCH v2 05/29] LoongArch: KVM: Add vcpu related header files

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Message-ID: <497693ca2cbc443c1d9f796c3aace6c9987bec72.camel@xry111.site>
Date:   Tue, 21 Feb 2023 12:44:52 +0800
From:   Xi Ruoyao <xry111@...111.site>
To:     Tianrui Zhao <zhaotianrui@...ngson.cn>,
        Paolo Bonzini <pbonzini@...hat.com>
Cc:     Huacai Chen <chenhuacai@...nel.org>,
        WANG Xuerui <kernel@...0n.name>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        loongarch@...ts.linux.dev, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org, Jens Axboe <axboe@...nel.dk>,
        Mark Brown <broonie@...nel.org>,
        Alex Deucher <alexander.deucher@....com>,
        Oliver Upton <oliver.upton@...ux.dev>, maobibo@...ngson.cn
Subject: Re: [PATCH v2 05/29] LoongArch: KVM: Add vcpu related header files

On Mon, 2023-02-20 at 14:57 +0800, Tianrui Zhao wrote:
> +/* GCSR */
> +static inline u64 gcsr_read(u32 reg)
> +{
> +       u64 val = 0;
> +
> +       asm volatile (
> +               "parse_r __reg, %[val]\n\t"
> +               ".word 0x5 << 24 | %[reg] << 10 | 0 << 5 | __reg\n\t"

Don't do this.  You should add the instruction to binutils first, then
make CONFIG_KVM depend on the assembler supporting this instruction. 
This is completely unreadable and only fine for an internal PoC.

> +               : [val] "+r" (val)
> +               : [reg] "i" (reg)
> +               : "memory");
> +
> +       return val;
> +}

-- 
Xi Ruoyao <xry111@...111.site>
School of Aerospace Science and Technology, Xidian University