Re: [PATCH v7 24/27] KVM: arm64/sve: Allow userspace to enable SVE for vcpus

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On Fri, Mar 29, 2019 at 01:00:49PM +0000, Dave Martin wrote:
> Now that all the pieces are in place, this patch offers a new flag
> KVM_ARM_VCPU_SVE that userspace can pass to KVM_ARM_VCPU_INIT to
> turn on SVE for the guest, on a per-vcpu basis.
> 
> As part of this, support for initialisation and reset of the SVE
> vector length set and registers is added in the appropriate places,
> as well as finally setting the KVM_ARM64_GUEST_HAS_SVE vcpu flag,
> to turn on the SVE support code.
> 
> Allocation of the SVE register storage in vcpu->arch.sve_state is
> deferred until the SVE configuration is finalized, by which time
> the size of the registers is known.
> 
> Setting the vector lengths supported by the vcpu is considered
> configuration of the emulated hardware rather than runtime
> configuration, so no support is offered for changing the vector
> lengths available to an existing vcpu across reset.
> 
> Signed-off-by: Dave Martin <Dave.Martin@xxxxxxx>
> Reviewed-by: Julien Thierry <julien.thierry@xxxxxxx>
> Tested-by: zhang.lei <zhang.lei@xxxxxxxxxxxxxx>
> 
> ---
> 
> Changes since v6:
> 
>  * [Kristina Martšenko] Amend comments explaining the
>    kvm_arm_vcpu_sve_finalized() versus !kvm_arm_vcpu_sve_finalized()
>    cases in kvm_reset_vcpu().
> 
>    Actually, I've just deleted the comments, since if anything they're
>    more confusing than the code they're supposed to describe.
> 
> Changes since v5:
> 
>  * Refactored to make the code flow clearer and clarify responsiblity
>    for the various initialisation phases/checks.
> 
>    In place of the previous, confusingly dual-purpose kvm_reset_sve(),
>    enabling and resetting of SVE are split into separate functions and
>    called as appropriate from kvm_reset_vcpu().
> 
>    To avoid interactions with preempt_disable(), memory allocation is
>    done in the kvm_vcpu_first_fun_init() path instead.  To achieve
>    this, the SVE memory allocation is moved to kvm_arm_vcpu_finalize(),
>    which now takes on the role of actually doing deferred setup instead
>    of just setting a flag to indicate that the setup was done.
> 
>  * Add has_vhe() sanity-check into kvm_vcpu_enable_sve(), since it
>    makes more sense here than when resetting the vcpu.
> 
>  * When checking for SVE finalization in kvm_reset_vcpu(), call the new
>    SVE-specific function kvm_arm_vcpu_sve_finalized().  The new generic
>    check kvm_arm_vcpu_is_finalized() is unnecessarily broad here: using
>    the appropriate specific check makes the code more self-describing.
> 
>  * Definition of KVM_ARM_VCPU_SVE moved to KVM: arm64/sve: Add pseudo-
>    register for the guest's vector lengths (which needs it for the
>    KVM_ARM_VCPU_FINALIZE ioctl).
> ---
>  arch/arm64/include/asm/kvm_host.h |  3 +--
>  arch/arm64/kvm/reset.c            | 43 ++++++++++++++++++++++++++++++++++++++-
>  2 files changed, 43 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
> index 5475cc4..9d57cf8 100644
> --- a/arch/arm64/include/asm/kvm_host.h
> +++ b/arch/arm64/include/asm/kvm_host.h
> @@ -49,8 +49,7 @@
>  
>  #define KVM_MAX_VCPUS VGIC_V3_MAX_CPUS
>  
> -/* Will be incremented when KVM_ARM_VCPU_SVE is fully implemented: */
> -#define KVM_VCPU_MAX_FEATURES 4
> +#define KVM_VCPU_MAX_FEATURES 5
>  
>  #define KVM_REQ_SLEEP \
>  	KVM_ARCH_REQ_FLAGS(0, KVM_REQUEST_WAIT | KVM_REQUEST_NO_WAKEUP)
> diff --git a/arch/arm64/kvm/reset.c b/arch/arm64/kvm/reset.c
> index e7f9c06..32c5ac0 100644
> --- a/arch/arm64/kvm/reset.c
> +++ b/arch/arm64/kvm/reset.c
> @@ -20,10 +20,12 @@
>   */
>  
>  #include <linux/errno.h>
> +#include <linux/kernel.h>
>  #include <linux/kvm_host.h>
>  #include <linux/kvm.h>
>  #include <linux/hw_breakpoint.h>
>  #include <linux/slab.h>
> +#include <linux/string.h>
>  #include <linux/types.h>
>  
>  #include <kvm/arm_arch_timer.h>
> @@ -37,6 +39,7 @@
>  #include <asm/kvm_coproc.h>
>  #include <asm/kvm_emulate.h>
>  #include <asm/kvm_mmu.h>
> +#include <asm/virt.h>
>  
>  /* Maximum phys_shift supported for any VM on this host */
>  static u32 kvm_ipa_limit;
> @@ -130,6 +133,27 @@ int kvm_arm_init_arch_resources(void)
>  	return 0;
>  }
>  
> +static int kvm_vcpu_enable_sve(struct kvm_vcpu *vcpu)
> +{
> +	if (!system_supports_sve())
> +		return -EINVAL;
> +
> +	/* Verify that KVM startup enforced this when SVE was detected: */
> +	if (WARN_ON(!has_vhe()))
> +		return -EINVAL;
> +
> +	vcpu->arch.sve_max_vl = kvm_sve_max_vl;
> +
> +	/*
> +	 * Userspace can still customize the vector lengths by writing
> +	 * KVM_REG_ARM64_SVE_VLS.  Allocation is deferred until
> +	 * kvm_arm_vcpu_finalize(), which freezes the configuration.
> +	 */
> +	vcpu->arch.flags |= KVM_ARM64_GUEST_HAS_SVE;
> +
> +	return 0;
> +}
> +
>  /*
>   * Finalize vcpu's maximum SVE vector length, allocating
>   * vcpu->arch.sve_state as necessary.
> @@ -188,13 +212,20 @@ void kvm_arch_vcpu_uninit(struct kvm_vcpu *vcpu)
>  	kfree(vcpu->arch.sve_state);
>  }
>  
> +static void kvm_vcpu_reset_sve(struct kvm_vcpu *vcpu)
> +{
> +	if (vcpu_has_sve(vcpu))
> +		memset(vcpu->arch.sve_state, 0, vcpu_sve_state_size(vcpu));
> +}
> +
>  /**
>   * kvm_reset_vcpu - sets core registers and sys_regs to reset value
>   * @vcpu: The VCPU pointer
>   *
>   * This function finds the right table above and sets the registers on
>   * the virtual CPU struct to their architecturally defined reset
> - * values.
> + * values, except for registers whose reset is deferred until
> + * kvm_arm_vcpu_finalize().
>   *
>   * Note: This function can be called from two paths: The KVM_ARM_VCPU_INIT
>   * ioctl or as part of handling a request issued by another VCPU in the PSCI
> @@ -217,6 +248,16 @@ int kvm_reset_vcpu(struct kvm_vcpu *vcpu)
>  	if (loaded)
>  		kvm_arch_vcpu_put(vcpu);
>  
> +	if (!kvm_arm_vcpu_sve_finalized(vcpu)) {
> +		if (test_bit(KVM_ARM_VCPU_SVE, vcpu->arch.features)) {
> +			ret = kvm_vcpu_enable_sve(vcpu);
> +			if (ret)
> +				goto out;
> +		}
> +	} else {
> +		kvm_vcpu_reset_sve(vcpu);
> +	}
> +
>  	switch (vcpu->arch.target) {
>  	default:
>  		if (test_bit(KVM_ARM_VCPU_EL1_32BIT, vcpu->arch.features)) {
> -- 
> 2.1.4
>

Reviewed-by: Andrew Jones <drjones@xxxxxxxxxx>
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