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Mon, 18 Jan 2021 05:07:36 -0800 (PST) Date: Mon, 18 Jan 2021 13:07:35 +0000 From: David Brazdil To: Marc Zyngier Cc: linux-arm-kernel@lists.infradead.org, kvmarm@lists.cs.columbia.edu, linux-kernel@vger.kernel.org, Catalin Marinas , Will Deacon , Mark Rutland , Alexandru Elisei , Ard Biesheuvel , Jing Zhang , Ajay Patil , Prasad Sodagudi , Srinivas Ramana , James Morse , Julien Thierry , Suzuki K Poulose , kernel-team@android.com Subject: Re: [PATCH v4 12/21] arm64: cpufeature: Add an early command-line cpufeature override facility Message-ID: <20210118130735.aor3g4eqxazf3mkq@google.com> References: <20210118094533.2874082-1-maz@kernel.org> <20210118094533.2874082-13-maz@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210118094533.2874082-13-maz@kernel.org> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Jan 18, 2021 at 09:45:24AM +0000, Marc Zyngier wrote: > In order to be able to override CPU features at boot time, > let's add a command line parser that matches options of the > form "cpureg.feature=value", and store the corresponding > value into the override val/mask pair. > > No features are currently defined, so no expected change in > functionality. > > Signed-off-by: Marc Zyngier Acked-by: David Brazdil > --- > arch/arm64/kernel/Makefile | 2 +- > arch/arm64/kernel/head.S | 1 + > arch/arm64/kernel/idreg-override.c | 119 +++++++++++++++++++++++++++++ > 3 files changed, 121 insertions(+), 1 deletion(-) > create mode 100644 arch/arm64/kernel/idreg-override.c > > diff --git a/arch/arm64/kernel/Makefile b/arch/arm64/kernel/Makefile > index 86364ab6f13f..2262f0392857 100644 > --- a/arch/arm64/kernel/Makefile > +++ b/arch/arm64/kernel/Makefile > @@ -17,7 +17,7 @@ obj-y := debug-monitors.o entry.o irq.o fpsimd.o \ > return_address.o cpuinfo.o cpu_errata.o \ > cpufeature.o alternative.o cacheinfo.o \ > smp.o smp_spin_table.o topology.o smccc-call.o \ > - syscall.o proton-pack.o > + syscall.o proton-pack.o idreg-override.o > > targets += efi-entry.o > > diff --git a/arch/arm64/kernel/head.S b/arch/arm64/kernel/head.S > index d74e5f84042e..b3c4dd04f74b 100644 > --- a/arch/arm64/kernel/head.S > +++ b/arch/arm64/kernel/head.S > @@ -435,6 +435,7 @@ SYM_FUNC_START_LOCAL(__primary_switched) > > mov x0, x21 // pass FDT address in x0 > bl early_fdt_map // Try mapping the FDT early > + bl init_shadow_regs > bl switch_to_vhe > #if defined(CONFIG_KASAN_GENERIC) || defined(CONFIG_KASAN_SW_TAGS) > bl kasan_early_init > diff --git a/arch/arm64/kernel/idreg-override.c b/arch/arm64/kernel/idreg-override.c > new file mode 100644 > index 000000000000..392f93b67103 > --- /dev/null > +++ b/arch/arm64/kernel/idreg-override.c > @@ -0,0 +1,119 @@ > +// SPDX-License-Identifier: GPL-2.0 > +/* > + * Early cpufeature override framework > + * > + * Copyright (C) 2020 Google LLC > + * Author: Marc Zyngier > + */ > + > +#include > +#include > + > +#include > +#include > + > +struct reg_desc { > + const char * const name; > + u64 * const val; > + u64 * const mask; > + struct { > + const char * const name; > + u8 shift; nit: There's an extra space before `shift`. > + } fields[]; > +}; > + > +static const struct reg_desc * const regs[] __initdata = { > +}; > + > +static int __init find_field(const char *cmdline, const struct reg_desc *reg, > + int f, u64 *v) > +{ > + char buf[256], *str; > + size_t len; > + > + snprintf(buf, ARRAY_SIZE(buf), "%s.%s=", reg->name, reg->fields[f].name); > + > + str = strstr(cmdline, buf); > + if (!(str == cmdline || (str > cmdline && *(str - 1) == ' '))) > + return -1; > + > + str += strlen(buf); > + len = strcspn(str, " "); > + len = min(len, ARRAY_SIZE(buf) - 1); > + strncpy(buf, str, len); > + buf[len] = 0; > + > + return kstrtou64(buf, 0, v); > +} > + > +static void __init match_options(const char *cmdline) > +{ > + int i; > + > + for (i = 0; i < ARRAY_SIZE(regs); i++) { > + int f; > + > + if (!regs[i]->val || !regs[i]->mask) > + continue; > + > + for (f = 0; regs[i]->fields[f].name; f++) { > + u64 v; > + > + if (find_field(cmdline, regs[i], f, &v)) > + continue; > + > + *regs[i]->val |= (v & 0xf) << regs[i]->fields[f].shift; > + *regs[i]->mask |= 0xfUL << regs[i]->fields[f].shift; > + } > + } > +} > + > +static __init void parse_cmdline(void) > +{ > + if (!IS_ENABLED(CONFIG_CMDLINE_FORCE)) { > + const u8 *prop; > + void *fdt; > + int node; > + > + fdt = get_early_fdt_ptr(); > + if (!fdt) > + goto out; > + > + node = fdt_path_offset(fdt, "/chosen"); > + if (node < 0) > + goto out; > + > + prop = fdt_getprop(fdt, node, "bootargs", NULL); > + if (!prop) > + goto out; > + > + match_options(prop); > + > + if (!IS_ENABLED(CONFIG_CMDLINE_EXTEND)) > + return; > + } > + > +out: > + match_options(CONFIG_CMDLINE); > +} > + > +void __init init_shadow_regs(void) > +{ > + int i; > + > + for (i = 0; i < ARRAY_SIZE(regs); i++) { > + if (regs[i]->val) > + *regs[i]->val = 0; > + if (regs[i]->mask) > + *regs[i]->mask = 0; > + } > + > + parse_cmdline(); > + > + for (i = 0; i < ARRAY_SIZE(regs); i++) { > + if (regs[i]->val) > + __flush_dcache_area(regs[i]->val, sizeof(*regs[i]->val)); > + if (regs[i]->mask) > + __flush_dcache_area(regs[i]->mask, sizeof(*regs[i]->mask)); > + } > +} > -- > 2.29.2 >