From: Sean Christopherson <seanjc@google.com>
To: Marc Orr <marcorr@google.com>
Cc: Chao Peng <chao.p.peng@linux.intel.com>,
Vishal Annapurve <vannapurve@google.com>,
x86@kernel.org, kvm@vger.kernel.org,
linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org,
pbonzini@redhat.com, vkuznets@redhat.com, wanpengli@tencent.com,
jmattson@google.com, joro@8bytes.org, tglx@linutronix.de,
mingo@redhat.com, bp@alien8.de, dave.hansen@linux.intel.com,
hpa@zytor.com, shuah@kernel.org, yang.zhong@intel.com,
ricarkol@google.com, aaronlewis@google.com, wei.w.wang@intel.com,
kirill.shutemov@linux.intel.com, corbet@lwn.net,
hughd@google.com, jlayton@kernel.org, bfields@fieldses.org,
akpm@linux-foundation.org, yu.c.zhang@linux.intel.com,
jun.nakajima@intel.com, dave.hansen@intel.com,
michael.roth@amd.com, qperret@google.com, steven.price@arm.com,
ak@linux.intel.com, david@redhat.com, luto@kernel.org,
vbabka@suse.cz, erdemaktas@google.com, pgonda@google.com,
nikunj@amd.com, diviness@google.com, maz@kernel.org,
dmatlack@google.com, axelrasmussen@google.com,
maciej.szmigiero@oracle.com, mizhang@google.com,
bgardon@google.com, ackerleytng@google.com
Subject: Re: [V1 PATCH 1/6] KVM: x86: Add support for testing private memory
Date: Mon, 28 Nov 2022 16:21:33 +0000 [thread overview]
Message-ID: <Y4TgDZPTXnnoTitB@google.com> (raw)
In-Reply-To: <CAA03e5EXU-TpZP2tyjEjfAAr9aNNcgmgOX6Rqv7ng+4Xc9H5AQ@mail.gmail.com>
On Wed, Nov 23, 2022, Marc Orr wrote:
> On Tue, Nov 22, 2022 at 12:06 PM Sean Christopherson <seanjc@google.com> wrote:
> > > > @@ -221,6 +220,9 @@ struct kvm_page_fault {
> > > > /* The memslot containing gfn. May be NULL. */
> > > > struct kvm_memory_slot *slot;
> > > >
> > > > + /* Derived from encryption bits of the faulting GPA for CVMs. */
> > > > + bool is_private;
> > >
> > > Either we can wrap it with the CONFIG_HAVE_KVM_PRIVATE_MEM_TESTING or if
> > > it looks ugly I can remove the "const" in my code.
> >
> > Hmm, I think we can keep the const. Similar to the bug in kvm_faultin_pfn()[*],
> > the kvm_slot_can_be_private() is bogus. A fault should be considered private if
> > it's marked as private, whether or not userspace has configured the slot to be
> > private is irrelevant. I.e. the xarray is the single source of truth, memslots
> > are just plumbing.
>
> If we incorporate Sean's suggestion and use xarray as the single
> source of truth, then can we get rid of the
> HAVE_KVM_PRIVATE_MEM_TESTING config?
No, we still want the opt-in config.
> Specifically, the self test can call the KVM_MEMORY_ENCRYPT_REG_REGION
> ioctl which will set the bits for the private FD within KVM's xarray.
Yes, but that should be disallowed for regular VMs without HAVE_KVM_PRIVATE_MEM_TESTING=y.
> (Maybe this was part of the point that Sean was making; but his
> feedback seemed focused on the discussion about keeping `is_private`
> const, whereas I've been staring at this trying to figure out if we
> can run the UPM selftests on a non-TDX/SNP VM WITHOUT a special
> test-only config. And Sean's idea seems to eliminate the need for the
> awkward CONFIG.)
"need" was always relative. It's obviously possible to enable any code without a
Kconfig, the question is whether or not it's a good idea to do so. In this case,
the answer is "no", because allowing private memory opens up a number a of code
paths and thus potential bugs. And we need something for kvm_arch_has_private_mem()
because returning "true" unconditionally is not correct for regular VMs.
next prev parent reply other threads:[~2022-11-28 16:21 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-11-11 1:42 [V1 PATCH 0/6] selftests: KVM: selftests for fd-based private memory Vishal Annapurve
2022-11-11 1:42 ` [V1 PATCH 1/6] KVM: x86: Add support for testing " Vishal Annapurve
2022-11-22 10:07 ` Chao Peng
2022-11-22 20:06 ` Sean Christopherson
2022-11-24 1:49 ` Marc Orr
2022-11-28 16:21 ` Sean Christopherson [this message]
2022-11-24 13:17 ` Chao Peng
2022-12-02 0:26 ` Michael Roth
2022-11-11 1:42 ` [V1 PATCH 2/6] KVM: Selftests: Add support for " Vishal Annapurve
2022-11-11 1:42 ` [V1 PATCH 3/6] KVM: selftests: x86: Add IS_ALIGNED/IS_PAGE_ALIGNED helpers Vishal Annapurve
2022-11-11 1:42 ` [V1 PATCH 4/6] KVM: selftests: x86: Execute VMs with private memory Vishal Annapurve
2022-11-14 19:37 ` Peter Gonda
2022-11-15 1:53 ` Vishal Annapurve
2022-12-08 21:56 ` Vishal Annapurve
2022-11-11 1:42 ` [V1 PATCH 5/6] KVM: selftests: Add get_free_huge_2m_pages Vishal Annapurve
2022-11-11 1:42 ` [V1 PATCH 6/6] KVM: selftests: x86: Add selftest for private memory Vishal Annapurve
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