On Mon, 04 Dec 2023 14:44:56 +0000, Mark Rutland <mark.rutland@xxxxxxx> wrote: > > On Mon, Dec 04, 2023 at 02:36:03PM +0000, Marc Zyngier wrote: > > ARMv8.2 introduced support for VPIPT i-caches, the V standing for > > VMID-tagged. Although this looked like a reasonable idea, no > > implementation has ever made it into the wild. > > > > Linux has supported this for over 6 years (amusingly, just as the > > architecture was dropping support for AIVIVT i-caches), but we had no > > way to even test it, and it is likely that this code was just > > bit-rotting. > > > > However, in a recent breakthrough (XML drop 2023-09, tagged as > > d55f5af8e09052abe92a02adf820deea2eaed717), the architecture has > > finally been purged of this option, making VIPT and PIPT the only two > > valid options. > > > > This really means this code is just dead code. Nobody will ever come > > up with such an implementation, and we can just get rid of it. > > > > Most of the impact is on KVM, where we drop a few large comment blocks > > (and a bit of code), while the core arch code loses the detection code > > itself. > > > > * From v2: > > - Fix reserved naming for RESERVED_AIVIVT > > - Collected RBs from Anshuman an Zenghui > > > > Marc Zyngier (3): > > KVM: arm64: Remove VPIPT I-cache handling > > arm64: Kill detection of VPIPT i-cache policy > > arm64: Rename reserved values for CTR_EL0.L1Ip > > For the series: > > Acked-by: Mark Rutland <mark.rutland@xxxxxxx> Thanks. > Looking forward, we can/should probably replace __icache_flags with a single > ICACHE_NOALIASING or ICACHE_PIPT cpucap, which'd get rid of a bunch of > duplicated logic and make that more sound in the case of races around cpu > onlining. As long as we refuse VIPT CPUs coming up late (i.e. after we have patched the kernel to set ICACHE_PIPT), it should be doable. I guess we already have this restriction as userspace is able to probe the I-cache policy anyway. How about the patch below (tested in a guest with a bunch of hacks to expose different L1Ip values)? Thanks, M. >From 8f88afb0b317213dcbf18ea460a508bfccc18568 Mon Sep 17 00:00:00 2001 From: Marc Zyngier <maz@xxxxxxxxxx> Date: Mon, 4 Dec 2023 18:09:40 +0000 Subject: [PATCH] arm64: Make icache detection a cpu capability Now that we only have two icache policies, we are in a good position to make the whole detection business more robust. Let's replace __icache_flags by a single capability (ICACHE_PIPT), and use this if all CPUs are indeed PIPT. It means we can rely on existing logic to mandate that a VIPT CPU coming up late will be denied booting, which is the safe thing to do. This also leads to some nice cleanups in pKVM, and KVM as a whole can use ARM64_ICACHE_PIPT as a final cap. Suggested-by: Mark Rutland <mark.rutland@xxxxxxx> Signed-off-by: Marc Zyngier <maz@xxxxxxxxxx> --- arch/arm64/include/asm/cache.h | 9 ++------- arch/arm64/include/asm/kvm_hyp.h | 1 - arch/arm64/include/asm/kvm_mmu.h | 2 +- arch/arm64/kernel/cpufeature.c | 7 +++++++ arch/arm64/kernel/cpuinfo.c | 34 -------------------------------- arch/arm64/kvm/arm.c | 1 - arch/arm64/kvm/hyp/nvhe/pkvm.c | 3 --- arch/arm64/tools/cpucaps | 1 + arch/arm64/tools/sysreg | 2 +- 9 files changed, 12 insertions(+), 48 deletions(-) diff --git a/arch/arm64/include/asm/cache.h b/arch/arm64/include/asm/cache.h index 06a4670bdb0b..8ef9522a6151 100644 --- a/arch/arm64/include/asm/cache.h +++ b/arch/arm64/include/asm/cache.h @@ -37,9 +37,9 @@ #ifndef __ASSEMBLY__ -#include <linux/bitops.h> #include <linux/kasan-enabled.h> +#include <asm/cpufeature.h> #include <asm/cputype.h> #include <asm/mte-def.h> #include <asm/sysreg.h> @@ -55,18 +55,13 @@ static inline unsigned int arch_slab_minalign(void) #define arch_slab_minalign() arch_slab_minalign() #endif -#define CTR_L1IP(ctr) SYS_FIELD_GET(CTR_EL0, L1Ip, ctr) - -#define ICACHEF_ALIASING 0 -extern unsigned long __icache_flags; - /* * Whilst the D-side always behaves as PIPT on AArch64, aliasing is * permitted in the I-cache. */ static inline int icache_is_aliasing(void) { - return test_bit(ICACHEF_ALIASING, &__icache_flags); + return !cpus_have_cap(ARM64_ICACHE_PIPT); } static inline u32 cache_type_cwg(void) diff --git a/arch/arm64/include/asm/kvm_hyp.h b/arch/arm64/include/asm/kvm_hyp.h index 145ce73fc16c..7ad70f9865fd 100644 --- a/arch/arm64/include/asm/kvm_hyp.h +++ b/arch/arm64/include/asm/kvm_hyp.h @@ -140,7 +140,6 @@ extern u64 kvm_nvhe_sym(id_aa64mmfr1_el1_sys_val); extern u64 kvm_nvhe_sym(id_aa64mmfr2_el1_sys_val); extern u64 kvm_nvhe_sym(id_aa64smfr0_el1_sys_val); -extern unsigned long kvm_nvhe_sym(__icache_flags); extern unsigned int kvm_nvhe_sym(kvm_arm_vmid_bits); #endif /* __ARM64_KVM_HYP_H__ */ diff --git a/arch/arm64/include/asm/kvm_mmu.h b/arch/arm64/include/asm/kvm_mmu.h index e3e793d0ec30..ab86c2f025cf 100644 --- a/arch/arm64/include/asm/kvm_mmu.h +++ b/arch/arm64/include/asm/kvm_mmu.h @@ -248,7 +248,7 @@ static inline void __invalidate_icache_guest_page(void *va, size_t size) * invalidation range exceeds our arbitrary limit on invadations by * cache line. */ - if (icache_is_aliasing() || size > __invalidate_icache_max_range()) + if (!cpus_have_final_cap(ARM64_ICACHE_PIPT) || size > __invalidate_icache_max_range()) icache_inval_all_pou(); else icache_inval_pou((unsigned long)va, (unsigned long)va + size); diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c index 646591c67e7a..73a37176676e 100644 --- a/arch/arm64/kernel/cpufeature.c +++ b/arch/arm64/kernel/cpufeature.c @@ -2272,6 +2272,13 @@ static const struct arm64_cpu_capabilities arm64_features[] = { .type = ARM64_CPUCAP_SYSTEM_FEATURE, .matches = has_always, }, + { + .desc = "PIPT I-cache policy", + .capability = ARM64_ICACHE_PIPT, + .type = ARM64_CPUCAP_SYSTEM_FEATURE, + .matches = has_cpuid_feature, + ARM64_CPUID_FIELDS(CTR_EL0, L1Ip, PIPT) + }, { .desc = "GIC system register CPU interface", .capability = ARM64_HAS_GIC_CPUIF_SYSREGS, diff --git a/arch/arm64/kernel/cpuinfo.c b/arch/arm64/kernel/cpuinfo.c index 47043c0d95ec..a4ea331fb6d4 100644 --- a/arch/arm64/kernel/cpuinfo.c +++ b/arch/arm64/kernel/cpuinfo.c @@ -33,20 +33,6 @@ DEFINE_PER_CPU(struct cpuinfo_arm64, cpu_data); static struct cpuinfo_arm64 boot_cpu_data; -static inline const char *icache_policy_str(int l1ip) -{ - switch (l1ip) { - case CTR_EL0_L1Ip_VIPT: - return "VIPT"; - case CTR_EL0_L1Ip_PIPT: - return "PIPT"; - default: - return "RESERVED/UNKNOWN"; - } -} - -unsigned long __icache_flags; - static const char *const hwcap_str[] = { [KERNEL_HWCAP_FP] = "fp", [KERNEL_HWCAP_ASIMD] = "asimd", @@ -378,24 +364,6 @@ static int __init cpuinfo_regs_init(void) } device_initcall(cpuinfo_regs_init); -static void cpuinfo_detect_icache_policy(struct cpuinfo_arm64 *info) -{ - unsigned int cpu = smp_processor_id(); - u32 l1ip = CTR_L1IP(info->reg_ctr); - - switch (l1ip) { - case CTR_EL0_L1Ip_PIPT: - break; - case CTR_EL0_L1Ip_VIPT: - default: - /* Assume aliasing */ - set_bit(ICACHEF_ALIASING, &__icache_flags); - break; - } - - pr_info("Detected %s I-cache on CPU%d\n", icache_policy_str(l1ip), cpu); -} - static void __cpuinfo_store_cpu_32bit(struct cpuinfo_32bit *info) { info->reg_id_dfr0 = read_cpuid(ID_DFR0_EL1); @@ -457,8 +425,6 @@ static void __cpuinfo_store_cpu(struct cpuinfo_arm64 *info) if (id_aa64pfr0_32bit_el0(info->reg_id_aa64pfr0)) __cpuinfo_store_cpu_32bit(&info->aarch32); - - cpuinfo_detect_icache_policy(info); } void cpuinfo_store_cpu(void) diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c index e5f75f1f1085..a5f71165cd5c 100644 --- a/arch/arm64/kvm/arm.c +++ b/arch/arm64/kvm/arm.c @@ -2242,7 +2242,6 @@ static void kvm_hyp_init_symbols(void) kvm_nvhe_sym(id_aa64mmfr1_el1_sys_val) = read_sanitised_ftr_reg(SYS_ID_AA64MMFR1_EL1); kvm_nvhe_sym(id_aa64mmfr2_el1_sys_val) = read_sanitised_ftr_reg(SYS_ID_AA64MMFR2_EL1); kvm_nvhe_sym(id_aa64smfr0_el1_sys_val) = read_sanitised_ftr_reg(SYS_ID_AA64SMFR0_EL1); - kvm_nvhe_sym(__icache_flags) = __icache_flags; kvm_nvhe_sym(kvm_arm_vmid_bits) = kvm_arm_vmid_bits; } diff --git a/arch/arm64/kvm/hyp/nvhe/pkvm.c b/arch/arm64/kvm/hyp/nvhe/pkvm.c index b29f15418c0a..187ce5720697 100644 --- a/arch/arm64/kvm/hyp/nvhe/pkvm.c +++ b/arch/arm64/kvm/hyp/nvhe/pkvm.c @@ -12,9 +12,6 @@ #include <nvhe/pkvm.h> #include <nvhe/trap_handler.h> -/* Used by icache_is_aliasing(). */ -unsigned long __icache_flags; - /* Used by kvm_get_vttbr(). */ unsigned int kvm_arm_vmid_bits; diff --git a/arch/arm64/tools/cpucaps b/arch/arm64/tools/cpucaps index b98c38288a9d..9c6313cd6f5e 100644 --- a/arch/arm64/tools/cpucaps +++ b/arch/arm64/tools/cpucaps @@ -53,6 +53,7 @@ HAS_TLB_RANGE HAS_VIRT_HOST_EXTN HAS_WFXT HW_DBM +ICACHE_PIPT KVM_HVHE KVM_PROTECTED_MODE MISMATCHED_CACHE_TYPE diff --git a/arch/arm64/tools/sysreg b/arch/arm64/tools/sysreg index c5af75b23187..db8c96841138 100644 --- a/arch/arm64/tools/sysreg +++ b/arch/arm64/tools/sysreg @@ -2003,7 +2003,7 @@ Field 28 IDC Field 27:24 CWG Field 23:20 ERG Field 19:16 DminLine -Enum 15:14 L1Ip +UnsignedEnum 15:14 L1Ip # This was named as VPIPT in the ARM but now documented as reserved 0b00 RESERVED_VPIPT # This is named as AIVIVT in the ARM but documented as reserved -- 2.39.2 -- Without deviation from the norm, progress is not possible.