linux-kernel - Re: [PATCH v3 0/7] KVM: Guest Memory Pre-Population API

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Date: Thu, 18 Apr 2024 00:01:03 +0000
From: "Edgecombe, Rick P" <rick.p.edgecombe@...el.com>
To: "kvm@...r.kernel.org" <kvm@...r.kernel.org>, "pbonzini@...hat.com"
	<pbonzini@...hat.com>, "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>
CC: "Li, Xiaoyao" <xiaoyao.li@...el.com>, "seanjc@...gle.com"
	<seanjc@...gle.com>, "binbin.wu@...ux.intel.com" <binbin.wu@...ux.intel.com>,
	"Yamahata, Isaku" <isaku.yamahata@...el.com>
Subject: Re: [PATCH v3 0/7] KVM: Guest Memory Pre-Population API

On Wed, 2024-04-17 at 11:34 -0400, Paolo Bonzini wrote:
> 
> Compared to Isaku's v2, I have reduced the scope as much as possible:
> 
> - no vendor-specific hooks

The TDX patches build on this, with the vendor callback looking like:

"
int tdx_pre_mmu_map_page(struct kvm_vcpu *vcpu,
			 struct kvm_map_memory *mapping,
			 u64 *error_code)
{
	struct kvm_tdx *kvm_tdx = to_kvm_tdx(vcpu->kvm);
	struct kvm *kvm = vcpu->kvm;

	if (!to_tdx(vcpu)->initialized)
		return -EINVAL;

	/* Shared-EPT case */
	if (!(kvm_is_private_gpa(kvm, mapping->base_address)))
		return 0;

	/* Once TD is finalized, the initial guest memory is fixed. */
	if (is_td_finalized(kvm_tdx))
		return -EINVAL;

	*error_code = TDX_SEPT_PFERR;
	return 0;
}
"

kvm_is_private_gpa() check is already handled in this series.

The initialized and finalized checks are nice guard rails for userspace, but
shouldn't be strictly required.

The TDX_SEPT_PFERR is (PFERR_WRITE_MASK | PFERR_PRIVATE_ACCESS). The
PFERR_WRITE_MASK doesn't seem to be required. Isaku, what was the intention?

But, I think maybe we should add a hook back in the TDX series for the guard
rails.