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

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Date:   Thu, 21 Nov 2019 23:22:12 +0800
From:   Yang Weijiang <weijiang.yang@...el.com>
To:     Paolo Bonzini <pbonzini@...hat.com>
Cc:     Yang Weijiang <weijiang.yang@...el.com>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, jmattson@...gle.com,
        sean.j.christopherson@...el.com, yu.c.zhang@...ux.intel.com,
        alazar@...defender.com, edwin.zhai@...el.com
Subject: Re: [PATCH v7 6/9] vmx: spp: Set up SPP paging table at
 vmentry/vmexit

On Thu, Nov 21, 2019 at 11:18:48AM +0100, Paolo Bonzini wrote:
> 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?
>
If the destination memory is SPP protected, the target memory is
expected unchanged on a "write op" in guest, so would like to skip current 
instruction.

> > +		pr_info("SPP - SPPT entry missing! gfn = 0x%llx\n", gfn);
> 
> Please replace pr_info with a tracepoint.
> 
OK.

> > +		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
>
OK.
> > +		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?
> 
Hmm, getting permission bits from gfn directly should work here. 
Thank you!

> > +	pr_alert("SPP - SPPT Misconfiguration!\n");
> > +	return 0;
> 
> 
> pr_alert not needed since you've just warned.
>
OK, will remove it.

> Paolo