linux-kernel - Re: [RFC V1 PATCH 0/5] selftests: KVM: selftests for fd-based approach of supporting private memory

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Date:   Mon, 11 Apr 2022 17:31:09 +0530
From:   "Nikunj A. Dadhania" <nikunj@....com>
To:     Vishal Annapurve <vannapurve@...gle.com>, x86@...nel.org,
        kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-kselftest@...r.kernel.org
Cc:     pbonzini@...hat.com, vkuznets@...hat.com, wanpengli@...cent.com,
        jmattson@...gle.com, joro@...tes.org, tglx@...utronix.de,
        mingo@...hat.com, bp@...en8.de, dave.hansen@...ux.intel.com,
        hpa@...or.com, shauh@...nel.org, yang.zhong@...el.com,
        drjones@...hat.com, ricarkol@...gle.com, aaronlewis@...gle.com,
        wei.w.wang@...el.com, kirill.shutemov@...ux.intel.com,
        corbet@....net, hughd@...gle.com, jlayton@...nel.org,
        bfields@...ldses.org, akpm@...ux-foundation.org,
        chao.p.peng@...ux.intel.com, yu.c.zhang@...ux.intel.com,
        jun.nakajima@...el.com, dave.hansen@...el.com,
        michael.roth@....com, qperret@...gle.com, steven.price@....com,
        ak@...ux.intel.com, david@...hat.com, luto@...nel.org,
        vbabka@...e.cz, marcorr@...gle.com, erdemaktas@...gle.com,
        pgonda@...gle.com, seanjc@...gle.com, diviness@...gle.com
Subject: Re: [RFC V1 PATCH 0/5] selftests: KVM: selftests for fd-based
 approach of supporting private memory

On 4/9/2022 2:35 AM, Vishal Annapurve wrote:
> This series implements selftests targeting the feature floated by Chao
> via:
> https://lore.kernel.org/linux-mm/20220310140911.50924-1-chao.p.peng@linux.intel.com/
> 

Thanks for working on this.

> Below changes aim to test the fd based approach for guest private memory
> in context of normal (non-confidential) VMs executing on non-confidential
> platforms.
> 
> Confidential platforms along with the confidentiality aware software
> stack support a notion of private/shared accesses from the confidential
> VMs.
> Generally, a bit in the GPA conveys the shared/private-ness of the
> access. Non-confidential platforms don't have a notion of private or
> shared accesses from the guest VMs. To support this notion,
> KVM_HC_MAP_GPA_RANGE
> is modified to allow marking an access from a VM within a GPA range as
> always shared or private. Any suggestions regarding implementing this ioctl
> alternatively/cleanly are appreciated.
> 
> priv_memfd_test.c file adds a suite of two basic selftests to access private
> memory from the guest via private/shared access and checking if the contents
> can be leaked to/accessed by vmm via shared memory view.
> 
> Test results:
> 1) PMPAT - PrivateMemoryPrivateAccess test passes
> 2) PMSAT - PrivateMemorySharedAccess test fails currently and needs more
> analysis to understand the reason of failure.

That could be because of the return code (*r = -1) from the KVM_EXIT_MEMORY_ERROR. 
This gets interpreted as -EPERM in the VMM when the vcpu_run exits.

	+	vcpu->run->exit_reason = KVM_EXIT_MEMORY_ERROR;
	+	vcpu->run->memory.flags = flags;
	+	vcpu->run->memory.padding = 0;
	+	vcpu->run->memory.gpa = fault->gfn << PAGE_SHIFT;
	+	vcpu->run->memory.size = PAGE_SIZE;
	+	fault->pfn = -1;
	+	*r = -1;
	+	return true;


Regards
Nikunj

[1] https://lore.kernel.org/all/20220310140911.50924-10-chao.p.peng@linux.intel.com/#t