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Date: Wed, 7 Aug 2019 18:47:53 +0000
From: Atish Patra <Atish.Patra@....com>
To: "paul.walmsley@...ive.com" <paul.walmsley@...ive.com>,
"rkrcmar@...hat.com" <rkrcmar@...hat.com>,
"pbonzini@...hat.com" <pbonzini@...hat.com>,
"palmer@...ive.com" <palmer@...ive.com>,
Anup Patel <Anup.Patel@....com>
CC: "linux-riscv@...ts.infradead.org" <linux-riscv@...ts.infradead.org>,
"daniel.lezcano@...aro.org" <daniel.lezcano@...aro.org>,
Alistair Francis <Alistair.Francis@....com>,
Damien Le Moal <Damien.LeMoal@....com>,
"hch@...radead.org" <hch@...radead.org>,
"tglx@...utronix.de" <tglx@...utronix.de>,
"anup@...infault.org" <anup@...infault.org>,
"kvm@...r.kernel.org" <kvm@...r.kernel.org>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v4 02/20] RISC-V: Add bitmap reprensenting ISA features
common across CPUs
On Wed, 2019-08-07 at 12:28 +0000, Anup Patel wrote:
> This patch adds riscv_isa bitmap which represents Host ISA features
> common across all Host CPUs. The riscv_isa is not same as elf_hwcap
> because elf_hwcap will only have ISA features relevant for user-space
> apps whereas riscv_isa will have ISA features relevant to both kernel
> and user-space apps.
>
> One of the use-case for riscv_isa bitmap is in KVM hypervisor where
> we will use it to do following operations:
>
> 1. Check whether hypervisor extension is available
> 2. Find ISA features that need to be virtualized (e.g. floating
> point support, vector extension, etc.)
>
> Signed-off-by: Anup Patel <anup.patel@....com>
> Signed-off-by: Atish Patra <atish.patra@....com>
> ---
> arch/riscv/include/asm/hwcap.h | 26 +++++++++++
> arch/riscv/kernel/cpufeature.c | 79
> ++++++++++++++++++++++++++++++++--
> 2 files changed, 102 insertions(+), 3 deletions(-)
>
> diff --git a/arch/riscv/include/asm/hwcap.h
> b/arch/riscv/include/asm/hwcap.h
> index 7ecb7c6a57b1..9b657375aa51 100644
> --- a/arch/riscv/include/asm/hwcap.h
> +++ b/arch/riscv/include/asm/hwcap.h
> @@ -8,6 +8,7 @@
> #ifndef __ASM_HWCAP_H
> #define __ASM_HWCAP_H
>
> +#include <linux/bits.h>
> #include <uapi/asm/hwcap.h>
>
> #ifndef __ASSEMBLY__
> @@ -22,5 +23,30 @@ enum {
> };
>
> extern unsigned long elf_hwcap;
> +
> +#define RISCV_ISA_EXT_a ('a' - 'a')
> +#define RISCV_ISA_EXT_c ('c' - 'a')
> +#define RISCV_ISA_EXT_d ('d' - 'a')
> +#define RISCV_ISA_EXT_f ('f' - 'a')
> +#define RISCV_ISA_EXT_h ('h' - 'a')
> +#define RISCV_ISA_EXT_i ('i' - 'a')
> +#define RISCV_ISA_EXT_m ('m' - 'a')
> +#define RISCV_ISA_EXT_s ('s' - 'a')
> +#define RISCV_ISA_EXT_u ('u' - 'a')
As per the discussion in following threads, 'S' & 'U' are not valid ISA
extensions. So we should drop them from here as well.
http://lists.infradead.org/pipermail/linux-riscv/2019-August/005771.html
https://lists.nongnu.org/archive/html/qemu-devel/2019-08/msg01217.html
> +#define RISCV_ISA_EXT_zicsr (('z' - 'a') + 1)
> +#define RISCV_ISA_EXT_zifencei (('z' - 'a') + 2)
> +#define RISCV_ISA_EXT_zam (('z' - 'a') + 3)
> +#define RISCV_ISA_EXT_ztso (('z' - 'a') + 4)
> +
> +#define RISCV_ISA_EXT_MAX 256
> +
> +unsigned long riscv_isa_extension_base(const unsigned long
> *isa_bitmap);
> +
> +#define riscv_isa_extension_mask(ext) BIT_MASK(RISCV_ISA_EXT_##ext)
> +
> +bool __riscv_isa_extension_available(const unsigned long
> *isa_bitmap, int bit);
> +#define riscv_isa_extension_available(isa_bitmap, ext) \
> + __riscv_isa_extension_available(isa_bitmap,
> RISCV_ISA_EXT_##ext)
> +
> #endif
> #endif
> diff --git a/arch/riscv/kernel/cpufeature.c
> b/arch/riscv/kernel/cpufeature.c
> index b1ade9a49347..4ce71ce5e290 100644
> --- a/arch/riscv/kernel/cpufeature.c
> +++ b/arch/riscv/kernel/cpufeature.c
> @@ -6,21 +6,64 @@
> * Copyright (C) 2017 SiFive
> */
>
> +#include <linux/bitmap.h>
> #include <linux/of.h>
> #include <asm/processor.h>
> #include <asm/hwcap.h>
> #include <asm/smp.h>
>
> unsigned long elf_hwcap __read_mostly;
> +
> +/* Host ISA bitmap */
> +static DECLARE_BITMAP(riscv_isa, RISCV_ISA_EXT_MAX) __read_mostly;
> +
> #ifdef CONFIG_FPU
> bool has_fpu __read_mostly;
> #endif
>
> +/**
> + * riscv_isa_extension_base - Get base extension word
> + *
> + * @isa_bitmap ISA bitmap to use
> + * @returns base extension word as unsigned long value
> + *
> + * NOTE: If isa_bitmap is NULL then Host ISA bitmap will be used.
> + */
> +unsigned long riscv_isa_extension_base(const unsigned long
> *isa_bitmap)
> +{
> + if (!isa_bitmap)
> + return riscv_isa[0];
> + return isa_bitmap[0];
> +}
> +EXPORT_SYMBOL_GPL(riscv_isa_extension_base);
> +
> +/**
> + * __riscv_isa_extension_available - Check whether given extension
> + * is available or not
> + *
> + * @isa_bitmap ISA bitmap to use
> + * @bit bit position of the desired extension
> + * @returns true or false
> + *
> + * NOTE: If isa_bitmap is NULL then Host ISA bitmap will be used.
> + */
> +bool __riscv_isa_extension_available(const unsigned long
> *isa_bitmap, int bit)
> +{
> + const unsigned long *bmap = (isa_bitmap) ? isa_bitmap :
> riscv_isa;
> +
> + if (bit >= RISCV_ISA_EXT_MAX)
> + return false;
> +
> + return test_bit(bit, bmap) ? true : false;
> +}
> +EXPORT_SYMBOL_GPL(__riscv_isa_extension_available);
> +
> void riscv_fill_hwcap(void)
> {
> struct device_node *node;
> const char *isa;
> - size_t i;
> + char print_str[BITS_PER_LONG+1];
> + size_t i, j, isa_len;
> static unsigned long isa2hwcap[256] = {0};
>
> isa2hwcap['i'] = isa2hwcap['I'] = COMPAT_HWCAP_ISA_I;
> @@ -32,8 +75,11 @@ void riscv_fill_hwcap(void)
>
> elf_hwcap = 0;
>
> + bitmap_zero(riscv_isa, RISCV_ISA_EXT_MAX);
> +
> for_each_of_cpu_node(node) {
> unsigned long this_hwcap = 0;
> + unsigned long this_isa = 0;
>
> if (riscv_of_processor_hartid(node) < 0)
> continue;
> @@ -43,8 +89,20 @@ void riscv_fill_hwcap(void)
> continue;
> }
>
> - for (i = 0; i < strlen(isa); ++i)
> + i = 0;
> + isa_len = strlen(isa);
> +#if defined(CONFIG_32BIT)
> + if (!strncmp(isa, "rv32", 4))
> + i += 4;
> +#elif defined(CONFIG_64BIT)
> + if (!strncmp(isa, "rv64", 4))
> + i += 4;
> +#endif
> + for (; i < isa_len; ++i) {
> this_hwcap |= isa2hwcap[(unsigned
> char)(isa[i])];
> + if ('a' <= isa[i] && isa[i] <= 'z')
> + this_isa |= (1UL << (isa[i] - 'a'));
> + }
>
> /*
> * All "okay" hart should have same isa. Set HWCAP
> based on
> @@ -55,6 +113,11 @@ void riscv_fill_hwcap(void)
> elf_hwcap &= this_hwcap;
> else
> elf_hwcap = this_hwcap;
> +
> + if (riscv_isa[0])
> + riscv_isa[0] &= this_isa;
> + else
> + riscv_isa[0] = this_isa;
> }
>
> /* We don't support systems with F but without D, so mask those
> out
> @@ -64,7 +127,17 @@ void riscv_fill_hwcap(void)
> elf_hwcap &= ~COMPAT_HWCAP_ISA_F;
> }
>
> - pr_info("elf_hwcap is 0x%lx\n", elf_hwcap);
> + memset(print_str, 0, sizeof(print_str));
> + for (i = 0, j = 0; i < BITS_PER_LONG; i++)
> + if (riscv_isa[0] & BIT_MASK(i))
> + print_str[j++] = (char)('a' + i);
> + pr_info("riscv: ISA extensions %s\n", print_str);
> +
> + memset(print_str, 0, sizeof(print_str));
> + for (i = 0, j = 0; i < BITS_PER_LONG; i++)
> + if (elf_hwcap & BIT_MASK(i))
> + print_str[j++] = (char)('a' + i);
> + pr_info("riscv: ELF capabilities %s\n", print_str);
>
> #ifdef CONFIG_FPU
> if (elf_hwcap & (COMPAT_HWCAP_ISA_F | COMPAT_HWCAP_ISA_D))
--
Regards,
Atish
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