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    Subject[PATCH 5.10 422/575] powerpc: Reintroduce is_kvm_guest() as a fast-path check
    Date
    From: Srikar Dronamraju <srikar@linux.vnet.ibm.com>

    [ Upstream commit a21d1becaa3f17a97b933ffa677b526afc514ec5 ]

    Introduce a static branch that would be set during boot if the OS
    happens to be a KVM guest. Subsequent checks to see if we are on KVM
    will rely on this static branch. This static branch would be used in
    vcpu_is_preempted() in a subsequent patch.

    Signed-off-by: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
    Acked-by: Waiman Long <longman@redhat.com>
    Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
    Link: https://lore.kernel.org/r/20201202050456.164005-4-srikar@linux.vnet.ibm.com
    Signed-off-by: Sasha Levin <sashal@kernel.org>
    ---
    arch/powerpc/include/asm/kvm_guest.h | 10 ++++++++++
    arch/powerpc/include/asm/kvm_para.h | 2 +-
    arch/powerpc/kernel/firmware.c | 2 ++
    3 files changed, 13 insertions(+), 1 deletion(-)

    diff --git a/arch/powerpc/include/asm/kvm_guest.h b/arch/powerpc/include/asm/kvm_guest.h
    index d7749ecb30d49..2fca299f7e192 100644
    --- a/arch/powerpc/include/asm/kvm_guest.h
    +++ b/arch/powerpc/include/asm/kvm_guest.h
    @@ -7,8 +7,18 @@
    #define _ASM_POWERPC_KVM_GUEST_H_

    #if defined(CONFIG_PPC_PSERIES) || defined(CONFIG_KVM_GUEST)
    +#include <linux/jump_label.h>
    +
    +DECLARE_STATIC_KEY_FALSE(kvm_guest);
    +
    +static inline bool is_kvm_guest(void)
    +{
    + return static_branch_unlikely(&kvm_guest);
    +}
    +
    bool check_kvm_guest(void);
    #else
    +static inline bool is_kvm_guest(void) { return false; }
    static inline bool check_kvm_guest(void) { return false; }
    #endif

    diff --git a/arch/powerpc/include/asm/kvm_para.h b/arch/powerpc/include/asm/kvm_para.h
    index 6fba06b6cfdbc..abe1b5e82547b 100644
    --- a/arch/powerpc/include/asm/kvm_para.h
    +++ b/arch/powerpc/include/asm/kvm_para.h
    @@ -14,7 +14,7 @@

    static inline int kvm_para_available(void)
    {
    - return IS_ENABLED(CONFIG_KVM_GUEST) && check_kvm_guest();
    + return IS_ENABLED(CONFIG_KVM_GUEST) && is_kvm_guest();
    }

    static inline unsigned int kvm_arch_para_features(void)
    diff --git a/arch/powerpc/kernel/firmware.c b/arch/powerpc/kernel/firmware.c
    index c3140c6084c93..c9e2819b095ab 100644
    --- a/arch/powerpc/kernel/firmware.c
    +++ b/arch/powerpc/kernel/firmware.c
    @@ -22,6 +22,7 @@ EXPORT_SYMBOL_GPL(powerpc_firmware_features);
    #endif

    #if defined(CONFIG_PPC_PSERIES) || defined(CONFIG_KVM_GUEST)
    +DEFINE_STATIC_KEY_FALSE(kvm_guest);
    bool check_kvm_guest(void)
    {
    struct device_node *hyper_node;
    @@ -33,6 +34,7 @@ bool check_kvm_guest(void)
    if (!of_device_is_compatible(hyper_node, "linux,kvm"))
    return false;

    + static_branch_enable(&kvm_guest);
    return true;
    }
    #endif
    --
    2.33.0


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