Re: [PATCH v7 6/9] vmx: spp: Set up SPP paging table at vmentry/vmexit

From: Paolo Bonzini <pbonzini@redhat.com>
To: Yang Weijiang <weijiang.yang@intel.com>,
	kvm@vger.kernel.org, linux-kernel@vger.kernel.org,
	jmattson@google.com, sean.j.christopherson@intel.com
Cc: yu.c.zhang@linux.intel.com, alazar@bitdefender.com, edwin.zhai@intel.com
Subject: Re: [PATCH v7 6/9] vmx: spp: Set up SPP paging table at vmentry/vmexit
Date: Thu, 21 Nov 2019 11:18:48 +0100	[thread overview]
Message-ID: <a7ce232b-0a54-0039-7009-8e92e8078791@redhat.com> (raw)
In-Reply-To: <20191119084949.15471-7-weijiang.yang@intel.com>

On 19/11/19 09:49, Yang Weijiang wrote:
> +			if (spte & PT_SPP_MASK) {
> +				fault_handled = true;
> +				vcpu->run->exit_reason = KVM_EXIT_SPP;
> +				vcpu->run->spp.addr = gva;
> +				kvm_skip_emulated_instruction(vcpu);

Do you really want to skip the current instruction?  Who will do the write?

> +		pr_info("SPP - SPPT entry missing! gfn = 0x%llx\n", gfn);

Please replace pr_info with a tracepoint.

> +		slot = gfn_to_memslot(vcpu->kvm, gfn);
> +		if (!slot)
> +			return -EFAULT;

You want either a goto to the misconfig case, so that there is a warn

> +		spp_info.base_gfn = gfn;
> +		spp_info.npages = 1;
> +
> +		spin_lock(&vcpu->kvm->mmu_lock);
> +		ret = kvm_spp_get_permission(vcpu->kvm, &spp_info);
> +		if (ret == 1) {

Can you clarify when ret will not be 1?  In this case you already have a
slot, so it seems to me that you do not need to go through
kvm_spp_get_permission and you can just test "if
(kvm->arch.spp_active)".  But then, spp_active should be 1 if you get
here, I think?

> +	pr_alert("SPP - SPPT Misconfiguration!\n");
> +	return 0;

pr_alert not needed since you've just warned.

Paolo