linux-kernel - Re: [PATCH v3 08/12] KVM: arm64: selftests: Add light-weight spinlock support

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Date:   Thu, 2 Sep 2021 14:06:58 -0700
From:   Oliver Upton <oupton@...gle.com>
To:     Raghavendra Rao Ananta <rananta@...gle.com>
Cc:     Paolo Bonzini <pbonzini@...hat.com>, Marc Zyngier <maz@...nel.org>,
        James Morse <james.morse@....com>,
        Alexandru Elisei <Alexandru.Elisei@....com>,
        Suzuki K Poulose <suzuki.poulose@....com>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>, Peter Shier <pshier@...gle.com>,
        Ricardo Koller <ricarkol@...gle.com>,
        Reiji Watanabe <reijiw@...gle.com>,
        Jing Zhang <jingzhangos@...gle.com>,
        linux-arm-kernel@...ts.infradead.org, kvmarm@...ts.cs.columbia.edu,
        linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Subject: Re: [PATCH v3 08/12] KVM: arm64: selftests: Add light-weight spinlock support

On Wed, Sep 1, 2021 at 2:14 PM Raghavendra Rao Ananta
<rananta@...gle.com> wrote:
>
> Add a simpler version of spinlock support for ARM64 for
> the guests to use.
>
> The implementation is loosely based on the spinlock
> implementation in kvm-unit-tests.
>
> Signed-off-by: Raghavendra Rao Ananta <rananta@...gle.com>
> ---
>  tools/testing/selftests/kvm/Makefile          |  2 +-
>  .../selftests/kvm/include/aarch64/spinlock.h  | 13 +++++++++
>  .../selftests/kvm/lib/aarch64/spinlock.c      | 27 +++++++++++++++++++
>  3 files changed, 41 insertions(+), 1 deletion(-)
>  create mode 100644 tools/testing/selftests/kvm/include/aarch64/spinlock.h
>  create mode 100644 tools/testing/selftests/kvm/lib/aarch64/spinlock.c
>
> diff --git a/tools/testing/selftests/kvm/Makefile b/tools/testing/selftests/kvm/Makefile
> index 5d05801ab816..61f0d376af99 100644
> --- a/tools/testing/selftests/kvm/Makefile
> +++ b/tools/testing/selftests/kvm/Makefile
> @@ -35,7 +35,7 @@ endif
>
>  LIBKVM = lib/assert.c lib/elf.c lib/io.c lib/kvm_util.c lib/rbtree.c lib/sparsebit.c lib/test_util.c lib/guest_modes.c lib/perf_test_util.c
>  LIBKVM_x86_64 = lib/x86_64/apic.c lib/x86_64/processor.c lib/x86_64/vmx.c lib/x86_64/svm.c lib/x86_64/ucall.c lib/x86_64/handlers.S
> -LIBKVM_aarch64 = lib/aarch64/processor.c lib/aarch64/ucall.c lib/aarch64/handlers.S
> +LIBKVM_aarch64 = lib/aarch64/processor.c lib/aarch64/ucall.c lib/aarch64/handlers.S lib/aarch64/spinlock.c
>  LIBKVM_s390x = lib/s390x/processor.c lib/s390x/ucall.c lib/s390x/diag318_test_handler.c
>
>  TEST_GEN_PROGS_x86_64 = x86_64/cr4_cpuid_sync_test
> diff --git a/tools/testing/selftests/kvm/include/aarch64/spinlock.h b/tools/testing/selftests/kvm/include/aarch64/spinlock.h
> new file mode 100644
> index 000000000000..cf0984106d14
> --- /dev/null
> +++ b/tools/testing/selftests/kvm/include/aarch64/spinlock.h
> @@ -0,0 +1,13 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +
> +#ifndef SELFTEST_KVM_ARM64_SPINLOCK_H
> +#define SELFTEST_KVM_ARM64_SPINLOCK_H
> +
> +struct spinlock {
> +       int v;
> +};
> +
> +extern void spin_lock(struct spinlock *lock);
> +extern void spin_unlock(struct spinlock *lock);
> +
> +#endif /* SELFTEST_KVM_ARM64_SPINLOCK_H */
> diff --git a/tools/testing/selftests/kvm/lib/aarch64/spinlock.c b/tools/testing/selftests/kvm/lib/aarch64/spinlock.c
> new file mode 100644
> index 000000000000..6d66a3dac237
> --- /dev/null
> +++ b/tools/testing/selftests/kvm/lib/aarch64/spinlock.c
> @@ -0,0 +1,27 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * ARM64 Spinlock support
> + */
> +#include <stdint.h>
> +
> +#include "spinlock.h"
> +
> +void spin_lock(struct spinlock *lock)
> +{
> +       uint32_t val, res;

nit: use 'int' to match the lock value type.

> +
> +       asm volatile(
> +       "1:     ldaxr   %w0, [%2]\n"
> +       "       cbnz    %w0, 1b\n"
> +       "       mov     %w0, #1\n"
> +       "       stxr    %w1, %w0, [%2]\n"
> +       "       cbnz    %w1, 1b\n"
> +       : "=&r" (val), "=&r" (res)
> +       : "r" (&lock->v)
> +       : "memory");
> +}
> +
> +void spin_unlock(struct spinlock *lock)
> +{
> +       asm volatile("stlr wzr, [%0]\n" : : "r" (&lock->v) : "memory");
> +}
> --
> 2.33.0.153.gba50c8fa24-goog
>

Otherwise, LGTM.

Reviewed-by: Oliver Upton <oupton@...gle.com>