• Christoffer Dall's avatar
    KVM: arm64: Avoid storing the vcpu pointer on the stack · 4464e210
    Christoffer Dall authored
    We already have the percpu area for the host cpu state, which points to
    the VCPU, so there's no need to store the VCPU pointer on the stack on
    every context switch.  We can be a little more clever and just use
    tpidr_el2 for the percpu offset and load the VCPU pointer from the host
    This has the benefit of being able to retrieve the host context even
    when our stack is corrupted, and it has a potential performance benefit
    because we trade a store plus a load for an mrs and a load on a round
    trip to the guest.
    This does require us to calculate the percpu offset without including
    the offset from the kernel mapping of the percpu array to the linear
    mapping of the array (which is what we store in tpidr_el1), because a
    PC-relative generated address in EL2 is already giving us the hyp alias
    of the linear mapping of a kernel address.  We do this in
    __cpu_init_hyp_mode() by using kvm_ksym_ref().
    The code that accesses ESR_EL2 was previously using an alternative to
    use the _EL1 accessor on VHE systems, but this was actually unnecessary
    as the _EL1 accessor aliases the ESR_EL2 register on VHE, and the _EL2
    accessor does the same thing on both systems.
    Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
    Reviewed-by: default avatarMarc Zyngier <marc.zyngier@arm.com>
    Reviewed-by: default avatarAndrew Jones <drjones@redhat.com>
    Signed-off-by: default avatarChristoffer Dall <christoffer.dall@linaro.org>
    Signed-off-by: default avatarMarc Zyngier <marc.zyngier@arm.com>
hyp-entry.S 5.51 KB