linux-kernel - Re: [PATCH v19 014/130] KVM: Add KVM vcpu ioctl to pre-populate guest memory

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Message-ID: <20240308210116.GB713729@ls.amr.corp.intel.com>
Date: Fri, 8 Mar 2024 13:01:16 -0800
From: Isaku Yamahata <isaku.yamahata@...el.com>
To: Yin Fengwei <fengwei.yin@...el.com>
Cc: isaku.yamahata@...el.com, kvm@...r.kernel.org,
	linux-kernel@...r.kernel.org, isaku.yamahata@...il.com,
	Paolo Bonzini <pbonzini@...hat.com>, erdemaktas@...gle.com,
	Sean Christopherson <seanjc@...gle.com>,
	Sagi Shahar <sagis@...gle.com>, Kai Huang <kai.huang@...el.com>,
	chen.bo@...el.com, hang.yuan@...el.com, tina.zhang@...el.com,
	isaku.yamahata@...ux.intel.com
Subject: Re: [PATCH v19 014/130] KVM: Add KVM vcpu ioctl to pre-populate
 guest memory

On Thu, Mar 07, 2024 at 03:01:11PM +0800,
Yin Fengwei <fengwei.yin@...el.com> wrote:

> > diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> > index 0349e1f241d1..2f0a8e28795e 100644
> > --- a/virt/kvm/kvm_main.c
> > +++ b/virt/kvm/kvm_main.c
> > @@ -4409,6 +4409,62 @@ static int kvm_vcpu_ioctl_get_stats_fd(struct kvm_vcpu *vcpu)
> >  	return fd;
> >  }
> >  
> > +__weak void kvm_arch_vcpu_pre_memory_mapping(struct kvm_vcpu *vcpu)
> > +{
> > +}
> > +
> > +__weak int kvm_arch_vcpu_memory_mapping(struct kvm_vcpu *vcpu,
> > +					struct kvm_memory_mapping *mapping)
> > +{
> > +	return -EOPNOTSUPP;
> > +}
> > +
> > +static int kvm_vcpu_memory_mapping(struct kvm_vcpu *vcpu,
> > +				   struct kvm_memory_mapping *mapping)
> > +{
> > +	bool added = false;
> > +	int idx, r = 0;
> > +
> > +	/* flags isn't used yet. */
> > +	if (mapping->flags)
> > +		return -EINVAL;
> > +
> > +	/* Sanity check */
> > +	if (!IS_ALIGNED(mapping->source, PAGE_SIZE) ||
> > +	    !mapping->nr_pages ||
> > +	    mapping->nr_pages & GENMASK_ULL(63, 63 - PAGE_SHIFT) ||
> > +	    mapping->base_gfn + mapping->nr_pages <= mapping->base_gfn)
> I suppose !mapping->nr_pages can be deleted as this line can cover it.
> > +		return -EINVAL;
> > +
> > +	vcpu_load(vcpu);
> > +	idx = srcu_read_lock(&vcpu->kvm->srcu);
> > +	kvm_arch_vcpu_pre_memory_mapping(vcpu);
> > +
> > +	while (mapping->nr_pages) {
> > +		if (signal_pending(current)) {
> > +			r = -ERESTARTSYS;
> > +			break;
> > +		}
> > +
> > +		if (need_resched())
> > +			cond_resched();
> > +
> > +		r = kvm_arch_vcpu_memory_mapping(vcpu, mapping);
> > +		if (r)
> > +			break;
> > +
> > +		added = true;
> > +	}
> > +
> > +	srcu_read_unlock(&vcpu->kvm->srcu, idx);
> > +	vcpu_put(vcpu);
> > +
> > +	if (added && mapping->nr_pages > 0)
> > +		r = -EAGAIN;
> > +
> > +	return r;
> > +}
> > +
> >  static long kvm_vcpu_ioctl(struct file *filp,
> >  			   unsigned int ioctl, unsigned long arg)
> >  {
> > @@ -4610,6 +4666,17 @@ static long kvm_vcpu_ioctl(struct file *filp,
> >  		r = kvm_vcpu_ioctl_get_stats_fd(vcpu);
> >  		break;
> >  	}
> > +	case KVM_MEMORY_MAPPING: {
> > +		struct kvm_memory_mapping mapping;
> > +
> > +		r = -EFAULT;
> > +		if (copy_from_user(&mapping, argp, sizeof(mapping)))
> > +			break;
> > +		r = kvm_vcpu_memory_mapping(vcpu, &mapping);
> return value r should be checked before copy_to_user

That's intentional to tell the mapping is partially or fully processed
regardless that error happened or not.

> 
> 
> Regards
> Yin, Fengwei
> 
> > +		if (copy_to_user(argp, &mapping, sizeof(mapping)))
> > +			r = -EFAULT;
> > +		break;
> > +	}
> >  	default:
> >  		r = kvm_arch_vcpu_ioctl(filp, ioctl, arg);
> >  	}
> 

-- 
Isaku Yamahata <isaku.yamahata@...el.com>