linux-kernel - Re: [PATCH 1/2] KVM: arm64: pkvm: Drop unnecessary FP/SIMD trap handler

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Date:   Tue, 10 May 2022 10:44:01 +0100
From:   Fuad Tabba <tabba@...gle.com>
To:     Oliver Upton <oupton@...gle.com>
Cc:     kvmarm@...ts.cs.columbia.edu, kvm@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        maz@...nel.org, james.morse@....com, alexandru.elisei@....com,
        suzuki.poulose@....com, qperret@...gle.com, will@...nel.org
Subject: Re: [PATCH 1/2] KVM: arm64: pkvm: Drop unnecessary FP/SIMD trap handler

Hi Oliver,

On Mon, May 9, 2022 at 5:26 PM Oliver Upton <oupton@...gle.com> wrote:
>
> The pVM-specific FP/SIMD trap handler just calls straight into the
> generic trap handler. Avoid the indirection and just call the hyp
> handler directly.
>
> Note that the BUILD_BUG_ON() pattern is repeated in
> pvm_init_traps_aa64pfr0(), which is likely a better home for it.
>
> No functional change intended.

Reviewed-by: Fuad Tabba <tabba@...gle.com>

Cheers,
/fuad

>
> Signed-off-by: Oliver Upton <oupton@...gle.com>
> ---
>  arch/arm64/kvm/hyp/nvhe/switch.c | 19 +------------------
>  1 file changed, 1 insertion(+), 18 deletions(-)
>
> diff --git a/arch/arm64/kvm/hyp/nvhe/switch.c b/arch/arm64/kvm/hyp/nvhe/switch.c
> index 6410d21d8695..3dee2ad96e10 100644
> --- a/arch/arm64/kvm/hyp/nvhe/switch.c
> +++ b/arch/arm64/kvm/hyp/nvhe/switch.c
> @@ -175,23 +175,6 @@ static bool kvm_handle_pvm_sys64(struct kvm_vcpu *vcpu, u64 *exit_code)
>                 kvm_handle_pvm_sysreg(vcpu, exit_code));
>  }
>
> -/**
> - * Handler for protected floating-point and Advanced SIMD accesses.
> - *
> - * Returns true if the hypervisor has handled the exit, and control should go
> - * back to the guest, or false if it hasn't.
> - */
> -static bool kvm_handle_pvm_fpsimd(struct kvm_vcpu *vcpu, u64 *exit_code)
> -{
> -       /* Linux guests assume support for floating-point and Advanced SIMD. */
> -       BUILD_BUG_ON(!FIELD_GET(ARM64_FEATURE_MASK(ID_AA64PFR0_FP),
> -                               PVM_ID_AA64PFR0_ALLOW));
> -       BUILD_BUG_ON(!FIELD_GET(ARM64_FEATURE_MASK(ID_AA64PFR0_ASIMD),
> -                               PVM_ID_AA64PFR0_ALLOW));
> -
> -       return kvm_hyp_handle_fpsimd(vcpu, exit_code);
> -}
> -
>  static const exit_handler_fn hyp_exit_handlers[] = {
>         [0 ... ESR_ELx_EC_MAX]          = NULL,
>         [ESR_ELx_EC_CP15_32]            = kvm_hyp_handle_cp15_32,
> @@ -207,7 +190,7 @@ static const exit_handler_fn pvm_exit_handlers[] = {
>         [0 ... ESR_ELx_EC_MAX]          = NULL,
>         [ESR_ELx_EC_SYS64]              = kvm_handle_pvm_sys64,
>         [ESR_ELx_EC_SVE]                = kvm_handle_pvm_restricted,
> -       [ESR_ELx_EC_FP_ASIMD]           = kvm_handle_pvm_fpsimd,
> +       [ESR_ELx_EC_FP_ASIMD]           = kvm_hyp_handle_fpsimd,
>         [ESR_ELx_EC_IABT_LOW]           = kvm_hyp_handle_iabt_low,
>         [ESR_ELx_EC_DABT_LOW]           = kvm_hyp_handle_dabt_low,
>         [ESR_ELx_EC_PAC]                = kvm_hyp_handle_ptrauth,
> --
> 2.36.0.512.ge40c2bad7a-goog
>