Re: [RFC PATCH 13/27] KVM: arm64: Enable access to sanitized CPU features at EL2

[Fuad Tabba]

Hi Quentin,

On Tue, Nov 17, 2020 at 6:16 PM 'Quentin Perret' via kernel-team
<kernel-team@xxxxxxxxxxx> wrote:
>
> Introduce the infrastructure in KVM enabling to copy CPU feature
> registers into EL2-owned data-structures, to allow reading sanitised
> values directly at EL2 in nVHE.
>
> Given that only a subset of these features are being read by the
> hypervisor, the ones that need to be copied are to be listed under
> <asm/kvm_cpufeature.h> together with the name of the nVHE variable that
> will hold the copy.
>
> While at it, introduce the first user of this infrastructure by
> implementing __flush_dcache_area at EL2, which needs
> arm64_ftr_reg_ctrel0.
>
> Signed-off-by: Quentin Perret <qperret@xxxxxxxxxx>
> ---
>  arch/arm64/include/asm/cpufeature.h     |  1 +
>  arch/arm64/include/asm/kvm_cpufeature.h | 17 ++++++++++++++
>  arch/arm64/kernel/cpufeature.c          | 12 ++++++++++
>  arch/arm64/kernel/image-vars.h          |  2 ++
>  arch/arm64/kvm/arm.c                    | 31 +++++++++++++++++++++++++
>  arch/arm64/kvm/hyp/nvhe/Makefile        |  3 ++-
>  arch/arm64/kvm/hyp/nvhe/cache.S         | 13 +++++++++++
>  arch/arm64/kvm/hyp/nvhe/cpufeature.c    |  8 +++++++
>  8 files changed, 86 insertions(+), 1 deletion(-)
>  create mode 100644 arch/arm64/include/asm/kvm_cpufeature.h
>  create mode 100644 arch/arm64/kvm/hyp/nvhe/cache.S
>  create mode 100644 arch/arm64/kvm/hyp/nvhe/cpufeature.c
>
> diff --git a/arch/arm64/include/asm/cpufeature.h b/arch/arm64/include/asm/cpufeature.h
> index da250e4741bd..3dfbd76fb647 100644
> --- a/arch/arm64/include/asm/cpufeature.h
> +++ b/arch/arm64/include/asm/cpufeature.h
> @@ -600,6 +600,7 @@ void __init setup_cpu_features(void);
>  void check_local_cpu_capabilities(void);
>
>  u64 read_sanitised_ftr_reg(u32 id);
> +int copy_ftr_reg(u32 id, struct arm64_ftr_reg *dst);
>
>  static inline bool cpu_supports_mixed_endian_el0(void)
>  {
> diff --git a/arch/arm64/include/asm/kvm_cpufeature.h b/arch/arm64/include/asm/kvm_cpufeature.h
> new file mode 100644
> index 000000000000..d34f85cba358
> --- /dev/null
> +++ b/arch/arm64/include/asm/kvm_cpufeature.h
> @@ -0,0 +1,17 @@
> +/* SPDX-License-Identifier: GPL-2.0-only */
> +/*
> + * Copyright (C) 2020 - Google LLC
> + * Author: Quentin Perret <qperret@xxxxxxxxxx>
> + */

Missing include guard.


> +
> +#include <asm/cpufeature.h>
> +
> +#ifndef KVM_HYP_CPU_FTR_REG
> +#if defined(__KVM_NVHE_HYPERVISOR__)
> +#define KVM_HYP_CPU_FTR_REG(id, name) extern struct arm64_ftr_reg name;
> +#else
> +#define KVM_HYP_CPU_FTR_REG(id, name) DECLARE_KVM_NVHE_SYM(name);
> +#endif
> +#endif
> +
> +KVM_HYP_CPU_FTR_REG(SYS_CTR_EL0, arm64_ftr_reg_ctrel0)
> diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
> index dd5bc0f0cf0d..3bc86d1423f8 100644
> --- a/arch/arm64/kernel/cpufeature.c
> +++ b/arch/arm64/kernel/cpufeature.c
> @@ -1116,6 +1116,18 @@ u64 read_sanitised_ftr_reg(u32 id)
>  }
>  EXPORT_SYMBOL_GPL(read_sanitised_ftr_reg);
>
> +int copy_ftr_reg(u32 id, struct arm64_ftr_reg *dst)
> +{
> +       struct arm64_ftr_reg *regp = get_arm64_ftr_reg(id);
> +
> +       if (!regp)
> +               return -EINVAL;
> +
> +       memcpy(dst, regp, sizeof(*regp));
> +
> +       return 0;
> +}
> +
>  #define read_sysreg_case(r)    \
>         case r:         return read_sysreg_s(r)
>
> diff --git a/arch/arm64/kernel/image-vars.h b/arch/arm64/kernel/image-vars.h
> index dd8ccc9efb6a..c35d768672eb 100644
> --- a/arch/arm64/kernel/image-vars.h
> +++ b/arch/arm64/kernel/image-vars.h
> @@ -116,6 +116,8 @@ __kvm_nvhe___memcpy                 = __kvm_nvhe___pi_memcpy;
>  __kvm_nvhe___memset                    = __kvm_nvhe___pi_memset;
>  #endif
>
> +_kvm_nvhe___flush_dcache_area          = __kvm_nvhe___pi___flush_dcache_area;
> +
>  #endif /* CONFIG_KVM */
>
>  #endif /* __ARM64_KERNEL_IMAGE_VARS_H */
> diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c
> index 391cf6753a13..c7f8fca97202 100644
> --- a/arch/arm64/kvm/arm.c
> +++ b/arch/arm64/kvm/arm.c
> @@ -34,6 +34,7 @@
>  #include <asm/virt.h>
>  #include <asm/kvm_arm.h>
>  #include <asm/kvm_asm.h>
> +#include <asm/kvm_cpufeature.h>
>  #include <asm/kvm_mmu.h>
>  #include <asm/kvm_emulate.h>
>  #include <asm/sections.h>
> @@ -1636,6 +1637,29 @@ static void teardown_hyp_mode(void)
>         }
>  }
>
> +#undef KVM_HYP_CPU_FTR_REG
> +#define KVM_HYP_CPU_FTR_REG(id, name) \
> +       { .sys_id = id, .dst = (struct arm64_ftr_reg *)&kvm_nvhe_sym(name) },
> +static const struct __ftr_reg_copy_entry {
> +       u32                     sys_id;
> +       struct arm64_ftr_reg    *dst;
> +} hyp_ftr_regs[] = {
> +       #include <asm/kvm_cpufeature.h>
> +};
> +
> +static int copy_cpu_ftr_regs(void)
> +{
> +       int i, ret;
> +
> +       for (i = 0; i < ARRAY_SIZE(hyp_ftr_regs); i++) {
> +               ret = copy_ftr_reg(hyp_ftr_regs[i].sys_id, hyp_ftr_regs[i].dst);
> +               if (ret)
> +                       return ret;
> +       }
> +
> +       return 0;
> +}
> +
>  /**
>   * Inits Hyp-mode on all online CPUs
>   */
> @@ -1644,6 +1668,13 @@ static int init_hyp_mode(void)
>         int cpu;
>         int err = 0;
>
> +       /*
> +        * Copy the required CPU feature register in their EL2 counterpart
> +        */
> +       err = copy_cpu_ftr_regs();
> +       if (err)
> +               return err;
> +
>         /*
>          * Allocate Hyp PGD and setup Hyp identity mapping
>          */
> diff --git a/arch/arm64/kvm/hyp/nvhe/Makefile b/arch/arm64/kvm/hyp/nvhe/Makefile
> index 9e5eacfec6ec..72cfe53f106f 100644
> --- a/arch/arm64/kvm/hyp/nvhe/Makefile
> +++ b/arch/arm64/kvm/hyp/nvhe/Makefile
> @@ -10,7 +10,8 @@ lib-objs := clear_page.o copy_page.o memcpy.o memset.o
>  lib-objs := $(addprefix ../../../lib/, $(lib-objs))
>
>  obj-y := timer-sr.o sysreg-sr.o debug-sr.o switch.o tlb.o hyp-init.o host.o \
> -        hyp-main.o hyp-smp.o psci-relay.o early_alloc.o stub.o page_alloc.o
> +        hyp-main.o hyp-smp.o psci-relay.o early_alloc.o stub.o page_alloc.o \
> +        cache.o cpufeature.o
>  obj-y += ../vgic-v3-sr.o ../aarch32.o ../vgic-v2-cpuif-proxy.o ../entry.o \
>          ../fpsimd.o ../hyp-entry.o ../exception.o
>  obj-y += $(lib-objs)
> diff --git a/arch/arm64/kvm/hyp/nvhe/cache.S b/arch/arm64/kvm/hyp/nvhe/cache.S
> new file mode 100644
> index 000000000000..36cef6915428
> --- /dev/null
> +++ b/arch/arm64/kvm/hyp/nvhe/cache.S
> @@ -0,0 +1,13 @@
> +/* SPDX-License-Identifier: GPL-2.0-only */
> +/*
> + * Code copied from arch/arm64/mm/cache.S.
> + */
> +
> +#include <linux/linkage.h>
> +#include <asm/assembler.h>
> +#include <asm/alternative.h>
> +
> +SYM_FUNC_START_PI(__flush_dcache_area)
> +       dcache_by_line_op civac, sy, x0, x1, x2, x3
> +       ret
> +SYM_FUNC_END_PI(__flush_dcache_area)
> diff --git a/arch/arm64/kvm/hyp/nvhe/cpufeature.c b/arch/arm64/kvm/hyp/nvhe/cpufeature.c
> new file mode 100644
> index 000000000000..a887508f996f
> --- /dev/null
> +++ b/arch/arm64/kvm/hyp/nvhe/cpufeature.c
> @@ -0,0 +1,8 @@
> +// SPDX-License-Identifier: GPL-2.0-only
> +/*
> + * Copyright (C) 2020 - Google LLC
> + * Author: Quentin Perret <qperret@xxxxxxxxxx>
> + */
> +
> +#define KVM_HYP_CPU_FTR_REG(id, name) struct arm64_ftr_reg name;
> +#include <asm/kvm_cpufeature.h>
> --
> 2.29.2.299.gdc1121823c-goog
>
> --
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>

/fuad