linux-kernel - Re: [RFC PATCH 2/8] KVM: Add KVM_MAP_MEMORY vcpu ioctl to pre-populate guest memory

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Date: Wed, 6 Mar 2024 16:49:19 -0800
From: David Matlack <dmatlack@...gle.com>
To: isaku.yamahata@...el.com
Cc: kvm@...r.kernel.org, isaku.yamahata@...il.com,
	linux-kernel@...r.kernel.org,
	Sean Christopherson <seanjc@...gle.com>,
	Paolo Bonzini <pbonzini@...hat.com>,
	Michael Roth <michael.roth@....com>,
	Federico Parola <federico.parola@...ito.it>
Subject: Re: [RFC PATCH 2/8] KVM: Add KVM_MAP_MEMORY vcpu ioctl to
 pre-populate guest memory

On 2024-03-01 09:28 AM, isaku.yamahata@...el.com wrote:
> From: Isaku Yamahata <isaku.yamahata@...el.com>
> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> index d1fd9cb5d037..d77c9b79d76b 100644
> --- a/virt/kvm/kvm_main.c
> +++ b/virt/kvm/kvm_main.c
> +static int kvm_vcpu_map_memory(struct kvm_vcpu *vcpu,
> +			       struct kvm_memory_mapping *mapping)
> +{
> +	bool added = false;
> +	int idx, r = 0;
> +
> +	if (mapping->flags & ~(KVM_MEMORY_MAPPING_FLAG_WRITE |
> +			       KVM_MEMORY_MAPPING_FLAG_EXEC |
> +			       KVM_MEMORY_MAPPING_FLAG_USER |
> +			       KVM_MEMORY_MAPPING_FLAG_PRIVATE))
> +		return -EINVAL;
> +	if ((mapping->flags & KVM_MEMORY_MAPPING_FLAG_PRIVATE) &&
> +	    !kvm_arch_has_private_mem(vcpu->kvm))
> +		return -EINVAL;
> +
> +	/* Sanity check */
> +	if (!IS_ALIGNED(mapping->source, PAGE_SIZE) ||
> +	    !mapping->nr_pages ||
> +	    mapping->base_gfn + mapping->nr_pages <= mapping->base_gfn)
> +		return -EINVAL;
> +
> +	vcpu_load(vcpu);
> +	idx = srcu_read_lock(&vcpu->kvm->srcu);
> +	r = kvm_arch_vcpu_pre_map_memory(vcpu);
> +	if (r)
> +		return r;
> +
> +	while (mapping->nr_pages) {
> +		if (signal_pending(current)) {
> +			r = -ERESTARTSYS;
> +			break;
> +		}
> +
> +		if (need_resched())

nit: Is need_resched() superfluous when calling cond_resched()?

> +			cond_resched();
> +
> +		r = kvm_arch_vcpu_map_memory(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;

This can overwrite the return value from kvm_arch_vcpu_map_memory().