Re: [PATCH v6 2/2] arm64: Add workaround for Arm Cortex-A77 erratum 1508412

Rob Herring
2020-10-20T14:42:40Z

On Thu, Sep 24, 2020 at 8:48 AM Rob Herring <robh@kernel.org> wrote:
>
> On Cortex-A77 r0p0 and r1p0, a sequence of a non-cacheable or device load
> and a store exclusive or PAR_EL1 read can cause a deadlock.
>
> The workaround requires a DMB SY before and after a PAR_EL1 register
> read. In addition, it's possible an interrupt (doing a device read) or
> KVM guest exit could be taken between the DMB and PAR read, so we
> also need a DMB before returning from interrupt and before returning to
> a guest.
>
> A deadlock is still possible with the workaround as KVM guests must also
> have the workaround. IOW, a malicious guest can deadlock an affected
> systems.
>
> This workaround also depends on a firmware counterpart to enable the h/w
> to insert DMB SY after load and store exclusive instructions. See the
> errata document SDEN-1152370 v10 [1] for more information.
>
> [1] https://static.docs.arm.com/101992/0010/Arm_Cortex_A77_MP074_Software_Developer_Errata_Notice_v10.pdf
>
> Cc: Catalin Marinas <catalin.marinas@arm.com>
> Cc: James Morse <james.morse@arm.com>
> Cc: Suzuki K Poulose <suzuki.poulose@arm.com>
> Cc: Will Deacon <will@kernel.org>
> Cc: Marc Zyngier <maz@kernel.org>
> Cc: Julien Thierry <julien.thierry.kdev@gmail.com>
> Cc: kvmarm@lists.cs.columbia.edu
> Signed-off-by: Rob Herring <robh@kernel.org>
> ---
> v6:
> - Do dmb on kernel_exit rather than disabling interrupts around PAR read
> v5:
> - Rebase on v5.9-rc3
> - Disable interrupts around PAR reads
> - Add DMB on return to guest
>
> v4:
> - Move read_sysreg_par out of KVM code to sysreg.h to share
> - Also use read_sysreg_par in fault.c and kvm/sys_regs.c
> - Use alternative f/w for dmbs around PAR read
> - Use cpus_have_final_cap instead of cpus_have_const_cap
> - Add note about speculation of PAR read
>
> v3:
> - Add dmbs around PAR reads in KVM code
> - Clean-up 'work-around' and 'errata'
>
> v2:
> - Don't disable KVM, just print warning
> ---
> Documentation/arm64/silicon-errata.rst | 2 ++
> arch/arm64/Kconfig | 20 ++++++++++++++++++++
> arch/arm64/include/asm/cpucaps.h | 3 ++-
> arch/arm64/include/asm/sysreg.h | 9 +++++++++
> arch/arm64/kernel/cpu_errata.c | 10 ++++++++++
> arch/arm64/kernel/entry.S | 3 +++
> arch/arm64/kvm/arm.c | 3 ++-
> arch/arm64/kvm/hyp/include/hyp/switch.h | 21 +++++++++++++--------
> arch/arm64/kvm/hyp/include/hyp/sysreg-sr.h | 2 +-
> arch/arm64/kvm/hyp/nvhe/switch.c | 2 +-
> arch/arm64/kvm/hyp/vhe/switch.c | 2 +-
> arch/arm64/kvm/sys_regs.c | 2 +-
> arch/arm64/mm/fault.c | 2 +-
> 13 files changed, 66 insertions(+), 15 deletions(-)

Marc, Can I get an ack for KVM on this? Will is waiting for one before applying.

Rob

>
> diff --git a/Documentation/arm64/silicon-errata.rst b/Documentation/arm64/silicon-errata.rst
> index d3587805de64..719510247292 100644
> --- a/Documentation/arm64/silicon-errata.rst
> +++ b/Documentation/arm64/silicon-errata.rst
> @@ -90,6 +90,8 @@ stable kernels.
> +----------------+-----------------+-----------------+-----------------------------+
> | ARM | Cortex-A76 | #1463225 | ARM64_ERRATUM_1463225 |
> +----------------+-----------------+-----------------+-----------------------------+
> +| ARM | Cortex-A77 | #1508412 | ARM64_ERRATUM_1508412 |
> ++----------------+-----------------+-----------------+-----------------------------+
> | ARM | Neoverse-N1 | #1188873,1418040| ARM64_ERRATUM_1418040 |
> +----------------+-----------------+-----------------+-----------------------------+
> | ARM | Neoverse-N1 | #1349291 | N/A |
> diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
> index 6d232837cbee..9ba14ff06cd6 100644
> --- a/arch/arm64/Kconfig
> +++ b/arch/arm64/Kconfig
> @@ -626,6 +626,26 @@ config ARM64_ERRATUM_1542419
>
> If unsure, say Y.
>
> +config ARM64_ERRATUM_1508412
> + bool "Cortex-A77: 1508412: workaround deadlock on sequence of NC/Device load and store exclusive or PAR read"
> + default y
> + help
> + This option adds a workaround for Arm Cortex-A77 erratum 1508412.
> +
> + Affected Cortex-A77 cores (r0p0, r1p0) could deadlock on a sequence
> + of a store-exclusive or read of PAR_EL1 and a load with device or
> + non-cacheable memory attributes. The workaround depends on a firmware
> + counterpart.
> +
> + KVM guests must also have the workaround implemented or they can
> + deadlock the system.
> +
> + Work around the issue by inserting DMB SY barriers around PAR_EL1
> + register reads and warning KVM users. The DMB barrier is sufficient
> + to prevent a speculative PAR_EL1 read.
> +
> + If unsure, say Y.
> +
> config CAVIUM_ERRATUM_22375
> bool "Cavium erratum 22375, 24313"
> default y
> diff --git a/arch/arm64/include/asm/cpucaps.h b/arch/arm64/include/asm/cpucaps.h
> index 07b643a70710..f184142b6e5a 100644
> --- a/arch/arm64/include/asm/cpucaps.h
> +++ b/arch/arm64/include/asm/cpucaps.h
> @@ -64,7 +64,8 @@
> #define ARM64_BTI 54
> #define ARM64_HAS_ARMv8_4_TTL 55
> #define ARM64_HAS_TLB_RANGE 56
> +#define ARM64_WORKAROUND_1508412 57
>
> -#define ARM64_NCAPS 57
> +#define ARM64_NCAPS 58
>
> #endif /* __ASM_CPUCAPS_H */
> diff --git a/arch/arm64/include/asm/sysreg.h b/arch/arm64/include/asm/sysreg.h
> index 554a7e8ecb07..d8a48d572c68 100644
> --- a/arch/arm64/include/asm/sysreg.h
> +++ b/arch/arm64/include/asm/sysreg.h
> @@ -943,6 +943,7 @@
>
> #include <linux/build_bug.h>
> #include <linux/types.h>
> +#include <asm/alternative.h>
>
> #define __DEFINE_MRS_MSR_S_REGNUM \
> " .irp num,0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30\n" \
> @@ -1024,6 +1025,14 @@
> write_sysreg(__scs_new, sysreg); \
> } while (0)
>
> +#define read_sysreg_par() ({ \
> + u64 par; \
> + asm(ALTERNATIVE("nop", "dmb sy", ARM64_WORKAROUND_1508412)); \
> + par = read_sysreg(par_el1); \
> + asm(ALTERNATIVE("nop", "dmb sy", ARM64_WORKAROUND_1508412)); \
> + par; \
> +})
> +
> #endif
>
> #endif /* __ASM_SYSREG_H */
> diff --git a/arch/arm64/kernel/cpu_errata.c b/arch/arm64/kernel/cpu_errata.c
> index c332d49780dc..b8ac7d1b2182 100644
> --- a/arch/arm64/kernel/cpu_errata.c
> +++ b/arch/arm64/kernel/cpu_errata.c
> @@ -952,6 +952,16 @@ const struct arm64_cpu_capabilities arm64_errata[] = {
> .matches = has_neoverse_n1_erratum_1542419,
> .cpu_enable = cpu_enable_trap_ctr_access,
> },
> +#endif
> +#ifdef CONFIG_ARM64_ERRATUM_1508412
> + {
> + /* we depend on the firmware portion for correctness */
> + .desc = "ARM erratum 1508412 (kernel portion)",
> + .capability = ARM64_WORKAROUND_1508412,
> + ERRATA_MIDR_RANGE(MIDR_CORTEX_A77,
> + 0, 0,
> + 1, 0),
> + },
> #endif
> {
> }
> diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S
> index 55af8b504b65..52232ee40634 100644
> --- a/arch/arm64/kernel/entry.S
> +++ b/arch/arm64/kernel/entry.S
> @@ -332,6 +332,9 @@ alternative_insn eret, nop, ARM64_UNMAP_KERNEL_AT_EL0
> br x30
> #endif
> .else
> + /* Ensure any device/NC reads complete */
> + alternative_insn nop, "dmb sy", ARM64_WORKAROUND_1508412
> +
> eret
> .endif
> sb
> diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c
> index 46dc3d75cf13..79ead5c510ab 100644
> --- a/arch/arm64/kvm/arm.c
> +++ b/arch/arm64/kvm/arm.c
> @@ -1640,7 +1640,8 @@ int kvm_arch_init(void *opaque)
> return -ENODEV;
> }
>
> - if (cpus_have_final_cap(ARM64_WORKAROUND_DEVICE_LOAD_ACQUIRE))
> + if (cpus_have_final_cap(ARM64_WORKAROUND_DEVICE_LOAD_ACQUIRE) ||
> + cpus_have_final_cap(ARM64_WORKAROUND_1508412))
> kvm_info("Guests without required CPU erratum workarounds can deadlock system!\n" \
> "Only trusted guests should be used on this system.\n");
>
> diff --git a/arch/arm64/kvm/hyp/include/hyp/switch.h b/arch/arm64/kvm/hyp/include/hyp/switch.h
> index 5b6b8fa00f0a..c48f4c59e933 100644
> --- a/arch/arm64/kvm/hyp/include/hyp/switch.h
> +++ b/arch/arm64/kvm/hyp/include/hyp/switch.h
> @@ -145,9 +145,9 @@ static inline bool __translate_far_to_hpfar(u64 far, u64 *hpfar)
> * We do need to save/restore PAR_EL1 though, as we haven't
> * saved the guest context yet, and we may return early...
> */
> - par = read_sysreg(par_el1);
> + par = read_sysreg_par();
> if (!__kvm_at("s1e1r", far))
> - tmp = read_sysreg(par_el1);
> + tmp = read_sysreg_par();
> else
> tmp = SYS_PAR_EL1_F; /* back to the guest */
> write_sysreg(par, par_el1);
> @@ -424,7 +424,7 @@ static inline bool fixup_guest_exit(struct kvm_vcpu *vcpu, u64 *exit_code)
> if (cpus_have_final_cap(ARM64_WORKAROUND_CAVIUM_TX2_219_TVM) &&
> kvm_vcpu_trap_get_class(vcpu) == ESR_ELx_EC_SYS64 &&
> handle_tx2_tvm(vcpu))
> - return true;
> + goto guest;
>
> /*
> * We trap the first access to the FP/SIMD to save the host context
> @@ -434,13 +434,13 @@ static inline bool fixup_guest_exit(struct kvm_vcpu *vcpu, u64 *exit_code)
> * Similarly for trapped SVE accesses.
> */
> if (__hyp_handle_fpsimd(vcpu))
> - return true;
> + goto guest;
>
> if (__hyp_handle_ptrauth(vcpu))
> - return true;
> + goto guest;
>
> if (!__populate_fault_info(vcpu))
> - return true;
> + goto guest;
>
> if (static_branch_unlikely(&vgic_v2_cpuif_trap)) {
> bool valid;
> @@ -455,7 +455,7 @@ static inline bool fixup_guest_exit(struct kvm_vcpu *vcpu, u64 *exit_code)
> int ret = __vgic_v2_perform_cpuif_access(vcpu);
>
> if (ret == 1)
> - return true;
> + goto guest;
>
> /* Promote an illegal access to an SError.*/
> if (ret == -1)
> @@ -471,12 +471,17 @@ static inline bool fixup_guest_exit(struct kvm_vcpu *vcpu, u64 *exit_code)
> int ret = __vgic_v3_perform_cpuif_access(vcpu);
>
> if (ret == 1)
> - return true;
> + goto guest;
> }
>
> exit:
> /* Return to the host kernel and handle the exit */
> return false;
> +
> +guest:
> + /* Re-enter the guest */
> + asm(ALTERNATIVE("nop", "dmb sy", ARM64_WORKAROUND_1508412));
> + return true;
> }
>
> static inline bool __needs_ssbd_off(struct kvm_vcpu *vcpu)
> diff --git a/arch/arm64/kvm/hyp/include/hyp/sysreg-sr.h b/arch/arm64/kvm/hyp/include/hyp/sysreg-sr.h
> index 7a986030145f..cce43bfe158f 100644
> --- a/arch/arm64/kvm/hyp/include/hyp/sysreg-sr.h
> +++ b/arch/arm64/kvm/hyp/include/hyp/sysreg-sr.h
> @@ -43,7 +43,7 @@ static inline void __sysreg_save_el1_state(struct kvm_cpu_context *ctxt)
> ctxt_sys_reg(ctxt, CONTEXTIDR_EL1) = read_sysreg_el1(SYS_CONTEXTIDR);
> ctxt_sys_reg(ctxt, AMAIR_EL1) = read_sysreg_el1(SYS_AMAIR);
> ctxt_sys_reg(ctxt, CNTKCTL_EL1) = read_sysreg_el1(SYS_CNTKCTL);
> - ctxt_sys_reg(ctxt, PAR_EL1) = read_sysreg(par_el1);
> + ctxt_sys_reg(ctxt, PAR_EL1) = read_sysreg_par();
> ctxt_sys_reg(ctxt, TPIDR_EL1) = read_sysreg(tpidr_el1);
>
> ctxt_sys_reg(ctxt, SP_EL1) = read_sysreg(sp_el1);
> diff --git a/arch/arm64/kvm/hyp/nvhe/switch.c b/arch/arm64/kvm/hyp/nvhe/switch.c
> index 0970442d2dbc..f4233cccf60b 100644
> --- a/arch/arm64/kvm/hyp/nvhe/switch.c
> +++ b/arch/arm64/kvm/hyp/nvhe/switch.c
> @@ -246,7 +246,7 @@ void __noreturn hyp_panic(struct kvm_cpu_context *host_ctxt)
> {
> u64 spsr = read_sysreg_el2(SYS_SPSR);
> u64 elr = read_sysreg_el2(SYS_ELR);
> - u64 par = read_sysreg(par_el1);
> + u64 par = read_sysreg_par();
> struct kvm_vcpu *vcpu = host_ctxt->__hyp_running_vcpu;
> unsigned long str_va;
>
> diff --git a/arch/arm64/kvm/hyp/vhe/switch.c b/arch/arm64/kvm/hyp/vhe/switch.c
> index c1da4f86ccac..c2cb27e57318 100644
> --- a/arch/arm64/kvm/hyp/vhe/switch.c
> +++ b/arch/arm64/kvm/hyp/vhe/switch.c
> @@ -212,7 +212,7 @@ void __noreturn hyp_panic(struct kvm_cpu_context *host_ctxt)
> {
> u64 spsr = read_sysreg_el2(SYS_SPSR);
> u64 elr = read_sysreg_el2(SYS_ELR);
> - u64 par = read_sysreg(par_el1);
> + u64 par = read_sysreg_par();
>
> __hyp_call_panic(spsr, elr, par, host_ctxt);
> unreachable();
> diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c
> index 077293b5115f..8d8d77794cc4 100644
> --- a/arch/arm64/kvm/sys_regs.c
> +++ b/arch/arm64/kvm/sys_regs.c
> @@ -95,7 +95,7 @@ static bool __vcpu_read_sys_reg_from_cpu(int reg, u64 *val)
> case AMAIR_EL1: *val = read_sysreg_s(SYS_AMAIR_EL12); break;
> case CNTKCTL_EL1: *val = read_sysreg_s(SYS_CNTKCTL_EL12); break;
> case ELR_EL1: *val = read_sysreg_s(SYS_ELR_EL12); break;
> - case PAR_EL1: *val = read_sysreg_s(SYS_PAR_EL1); break;
> + case PAR_EL1: *val = read_sysreg_par(); break;
> case DACR32_EL2: *val = read_sysreg_s(SYS_DACR32_EL2); break;
> case IFSR32_EL2: *val = read_sysreg_s(SYS_IFSR32_EL2); break;
> case DBGVCR32_EL2: *val = read_sysreg_s(SYS_DBGVCR32_EL2); break;
> diff --git a/arch/arm64/mm/fault.c b/arch/arm64/mm/fault.c
> index f07333e86c2f..2dbd1d9aa3c7 100644
> --- a/arch/arm64/mm/fault.c
> +++ b/arch/arm64/mm/fault.c
> @@ -260,7 +260,7 @@ static bool __kprobes is_spurious_el1_translation_fault(unsigned long addr,
> local_irq_save(flags);
> asm volatile("at s1e1r, %0" :: "r" (addr));
> isb();
> - par = read_sysreg(par_el1);
> + par = read_sysreg_par();
> local_irq_restore(flags);
>
> /*
> --
> 2.25.1