Message-ID: <4cd00b5cdc78da6357d2d326e607b169faee34a8.camel@xry111.site>
Subject: Re: [PATCH v2 05/29] LoongArch: KVM: Add vcpu related header files
From:   Xi Ruoyao <xry111@xry111.site>
To:     maobibo <maobibo@loongson.cn>,
        Tianrui Zhao <zhaotianrui@loongson.cn>,
        Paolo Bonzini <pbonzini@redhat.com>
Cc:     Huacai Chen <chenhuacai@kernel.org>,
        WANG Xuerui <kernel@xen0n.name>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        loongarch@lists.linux.dev, linux-kernel@vger.kernel.org,
        kvm@vger.kernel.org, Jens Axboe <axboe@kernel.dk>,
        Mark Brown <broonie@kernel.org>,
        Alex Deucher <alexander.deucher@amd.com>,
        Oliver Upton <oliver.upton@linux.dev>
Date:   Tue, 21 Feb 2023 15:12:16 +0800
In-Reply-To: <7d6125dd-29e8-14d8-b1d7-d8c14d7bec80@loongson.cn>
References: <20230220065735.1282809-1-zhaotianrui@loongson.cn>
         <20230220065735.1282809-6-zhaotianrui@loongson.cn>
         <497693ca2cbc443c1d9f796c3aace6c9987bec72.camel@xry111.site>
         <7d6125dd-29e8-14d8-b1d7-d8c14d7bec80@loongson.cn>
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On Tue, 2023-02-21 at 14:46 +0800, maobibo wrote:
> > On Mon, 2023-02-20 at 14:57 +0800, Tianrui Zhao wrote:
> > > +/* GCSR */
> > > +static inline u64 gcsr_read(u32 reg)
> > > +{
> > > +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0u64 val =3D 0;
> > > +
> > > +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0asm volatile (
> > > +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=
=C2=A0=C2=A0=C2=A0=C2=A0"parse_r __reg, %[val]\n\t"
> > > +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=
=C2=A0=C2=A0=C2=A0=C2=A0".word 0x5 << 24 | %[reg] << 10 | 0 << 5 | __reg\n\=
t"
> >=20
> > Don't do this.=C2=A0 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.
>=20
> We are preparing to submit these instruction support for binutils,
> however it is still necessary. Supposing that it is supported in future
> gcc version, we can not drop existing gcc 12/13 supporting to compiling
> kernel with LoongArch architecture.

You can drop the support for KVM with less capable Binutils versions,
like:

config AS_HAS_LVZ
    def_bool $(as-instr some_gcsr_insn \$r0, \$gcsr0)

config KVM
    depends on AS_HAS_LVZ

>=20
> Maybe there will be human readable code like this:
> #if GCC_SUPPORT_KVM_INSTR
> =C2=A0 ...
> #else
> =C2=A0 asm volatile (".word=C2=A0=C2=A0 "
> =C2=A0 ...
> #endif
>=20
> Regards
> Bibo, Mao

--=20
Xi Ruoyao <xry111@xry111.site>
School of Aerospace Science and Technology, Xidian University