linux-kernel - Re: [PATCH v7 4/9] mmu: spp: Add functions to create/destroy SPP bitmap block

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Message-ID: <8ad27209-cc28-0503-da0e-bead63b28a83@redhat.com>
Date:   Thu, 21 Nov 2019 11:43:10 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Yang Weijiang <weijiang.yang@...el.com>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, jmattson@...gle.com,
        sean.j.christopherson@...el.com
Cc:     yu.c.zhang@...ux.intel.com, alazar@...defender.com,
        edwin.zhai@...el.com
Subject: Re: [PATCH v7 4/9] mmu: spp: Add functions to create/destroy SPP
 bitmap block

On 19/11/19 09:49, Yang Weijiang wrote:
>  
> +/*
> + * all vcpus share the same SPPT, vcpu->arch.mmu->sppt_root points to same
> + * SPPT root page, so any vcpu will do.
> + */
> +static struct kvm_vcpu *kvm_spp_get_vcpu(struct kvm *kvm)
> +{
> +	struct kvm_vcpu *vcpu = NULL;
> +	int idx;

Is this true?  Perhaps you need one with
VALID_PAGE(vcpu->arch.mmu->sppt_root) for kvm_spp_set_permission?

Also, since vcpu->arch.mmu->sppt_root is the same for all vCPUs, perhaps
it should be kvm->arch.sppt_root instead?

If you can get rid of this function, it would be much better (but if you
cannot, kvm_get_vcpu(kvm, 0) should give the same result).

> 
> +	if (npages > SUBPAGE_MAX_BITMAP)
> +		return -EFAULT;

This is not needed here, the restriction only applies to the ioctl.

Paolo