From: Sean Christopherson <seanjc@google.com>
To: Xiaoyao Li <xiaoyao.li@intel.com>
Cc: Michael Roth <michael.roth@amd.com>,
Vishal Annapurve <vannapurve@google.com>,
Chao Peng <chao.p.peng@linux.intel.com>,
"Nikunj A. Dadhania" <nikunj@amd.com>,
kvm list <kvm@vger.kernel.org>,
LKML <linux-kernel@vger.kernel.org>,
linux-mm@kvack.org, linux-fsdevel@vger.kernel.org,
linux-api@vger.kernel.org, linux-doc@vger.kernel.org,
qemu-devel@nongnu.org, Paolo Bonzini <pbonzini@redhat.com>,
Jonathan Corbet <corbet@lwn.net>,
Vitaly Kuznetsov <vkuznets@redhat.com>,
Wanpeng Li <wanpengli@tencent.com>,
Jim Mattson <jmattson@google.com>, Joerg Roedel <joro@8bytes.org>,
Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
x86 <x86@kernel.org>, "H . Peter Anvin" <hpa@zytor.com>,
Hugh Dickins <hughd@google.com>, Jeff Layton <jlayton@kernel.org>,
"J . Bruce Fields" <bfields@fieldses.org>,
Andrew Morton <akpm@linux-foundation.org>,
Mike Rapoport <rppt@kernel.org>,
Steven Price <steven.price@arm.com>,
"Maciej S . Szmigiero" <mail@maciej.szmigiero.name>,
Vlastimil Babka <vbabka@suse.cz>,
Yu Zhang <yu.c.zhang@linux.intel.com>,
"Kirill A . Shutemov" <kirill.shutemov@linux.intel.com>,
Andy Lutomirski <luto@kernel.org>,
Jun Nakajima <jun.nakajima@intel.com>,
Dave Hansen <dave.hansen@intel.com>,
Andi Kleen <ak@linux.intel.com>,
David Hildenbrand <david@redhat.com>,
aarcange@redhat.com, ddutile@redhat.com, dhildenb@redhat.com,
Quentin Perret <qperret@google.com>,
mhocko@suse.com
Subject: Re: [PATCH v6 6/8] KVM: Handle page fault for private memory
Date: Thu, 7 Jul 2022 20:08:04 +0000 [thread overview]
Message-ID: <Ysc9JDcVAnlVrGC8@google.com> (raw)
In-Reply-To: <4fe3b47d-e94a-890a-5b87-6dfb7763bc7e@intel.com>
On Fri, Jul 01, 2022, Xiaoyao Li wrote:
> On 7/1/2022 6:21 AM, Michael Roth wrote:
> > On Thu, Jun 30, 2022 at 12:14:13PM -0700, Vishal Annapurve wrote:
> > > With transparent_hugepages=always setting I see issues with the
> > > current implementation.
...
> > > Looks like with transparent huge pages enabled kvm tried to handle the
> > > shared memory fault on 0x84d gfn by coalescing nearby 4K pages
> > > to form a contiguous 2MB page mapping at gfn 0x800, since level 2 was
> > > requested in kvm_mmu_spte_requested.
> > > This caused the private memory contents from regions 0x800-0x84c and
> > > 0x86e-0xa00 to get unmapped from the guest leading to guest vm
> > > shutdown.
> >
> > Interesting... seems like that wouldn't be an issue for non-UPM SEV, since
> > the private pages would still be mapped as part of that 2M mapping, and
> > it's completely up to the guest as to whether it wants to access as
> > private or shared. But for UPM it makes sense this would cause issues.
> >
> > >
> > > Does getting the mapping level as per the fault access type help
> > > address the above issue? Any such coalescing should not cross between
> > > private to
> > > shared or shared to private memory regions.
> >
> > Doesn't seem like changing the check to fault->is_private would help in
> > your particular case, since the subsequent host_pfn_mapping_level() call
> > only seems to limit the mapping level to whatever the mapping level is
> > for the HVA in the host page table.
> >
> > Seems like with UPM we need some additional handling here that also
> > checks that the entire 2M HVA range is backed by non-private memory.
> >
> > Non-UPM SNP hypervisor patches already have a similar hook added to
> > host_pfn_mapping_level() which implements such a check via RMP table, so
> > UPM might need something similar:
> >
> > https://github.com/AMDESE/linux/commit/ae4475bc740eb0b9d031a76412b0117339794139
> >
> > -Mike
> >
>
> For TDX, we try to track the page type (shared, private, mixed) of each gfn
> at given level. Only when the type is shared/private, can it be mapped at
> that level. When it's mixed, i.e., it contains both shared pages and private
> pages at given level, it has to go to next smaller level.
>
> https://github.com/intel/tdx/commit/ed97f4042eb69a210d9e972ccca6a84234028cad
Hmm, so a new slot->arch.page_attr array shouldn't be necessary, KVM can instead
update slot->arch.lpage_info on shared<->private conversions. Detecting whether
a given range is partially mapped could get nasty if KVM defers tracking to the
backing store, but if KVM itself does the tracking as was previously suggested[*],
then updating lpage_info should be relatively straightfoward, e.g. use
xa_for_each_range() to see if a given 2mb/1gb range is completely covered (fully
shared) or not covered at all (fully private).
[*] https://lore.kernel.org/all/YofeZps9YXgtP3f1@google.com
next prev parent reply other threads:[~2022-07-07 20:08 UTC|newest]
Thread overview: 58+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-05-19 15:37 [PATCH v6 0/8] KVM: mm: fd-based approach for supporting KVM guest private memory Chao Peng
2022-05-19 15:37 ` [PATCH v6 1/8] mm: Introduce memfile_notifier Chao Peng
2022-05-19 15:37 ` [PATCH v6 2/8] mm/shmem: Support memfile_notifier Chao Peng
2022-05-19 15:37 ` [PATCH v6 3/8] mm/memfd: Introduce MFD_INACCESSIBLE flag Chao Peng
2022-05-31 19:15 ` Vishal Annapurve
2022-06-01 10:17 ` Chao Peng
2022-06-01 12:11 ` Gupta, Pankaj
2022-06-02 10:07 ` Chao Peng
2022-06-14 20:23 ` Sean Christopherson
2022-06-15 8:53 ` Chao Peng
2022-05-19 15:37 ` [PATCH v6 4/8] KVM: Extend the memslot to support fd-based private memory Chao Peng
2022-05-20 17:57 ` Andy Lutomirski
2022-05-20 18:31 ` Sean Christopherson
2022-05-22 4:03 ` Andy Lutomirski
2022-05-23 13:21 ` Chao Peng
2022-05-23 15:22 ` Sean Christopherson
2022-05-30 13:26 ` Chao Peng
2022-06-10 16:14 ` Sean Christopherson
2022-06-14 6:45 ` Chao Peng
2022-06-23 22:59 ` Michael Roth
2022-06-24 8:54 ` Chao Peng
2022-06-24 13:01 ` Michael Roth
2022-06-17 20:52 ` Sean Christopherson
2022-06-17 21:27 ` Sean Christopherson
2022-06-20 14:09 ` Chao Peng
2022-06-20 14:08 ` Chao Peng
2022-05-19 15:37 ` [PATCH v6 5/8] KVM: Add KVM_EXIT_MEMORY_FAULT exit Chao Peng
2022-05-19 15:37 ` [PATCH v6 6/8] KVM: Handle page fault for private memory Chao Peng
2022-06-17 21:30 ` Sean Christopherson
2022-06-20 14:16 ` Chao Peng
2022-08-19 0:40 ` Kirill A. Shutemov
2022-08-25 23:43 ` Sean Christopherson
2022-06-24 3:58 ` Nikunj A. Dadhania
2022-06-24 9:02 ` Chao Peng
2022-06-30 19:14 ` Vishal Annapurve
2022-06-30 22:21 ` Michael Roth
2022-07-01 1:21 ` Xiaoyao Li
2022-07-07 20:08 ` Sean Christopherson [this message]
2022-07-08 3:29 ` Xiaoyao Li
2022-07-20 23:08 ` Vishal Annapurve
2022-07-21 9:45 ` Chao Peng
2022-05-19 15:37 ` [PATCH v6 7/8] KVM: Enable and expose KVM_MEM_PRIVATE Chao Peng
2022-06-23 22:07 ` Michael Roth
2022-06-24 8:43 ` Chao Peng
2022-05-19 15:37 ` [PATCH v6 8/8] memfd_create.2: Describe MFD_INACCESSIBLE flag Chao Peng
2022-06-06 20:09 ` [PATCH v6 0/8] KVM: mm: fd-based approach for supporting KVM guest private memory Vishal Annapurve
2022-06-07 6:57 ` Chao Peng
2022-06-08 0:55 ` Marc Orr
2022-06-08 2:18 ` Chao Peng
2022-06-08 19:37 ` Vishal Annapurve
2022-06-09 20:29 ` Sean Christopherson
2022-06-14 7:28 ` Chao Peng
2022-06-14 17:37 ` Andy Lutomirski
2022-06-14 19:08 ` Sean Christopherson
2022-06-14 20:59 ` Andy Lutomirski
2022-06-15 9:17 ` Chao Peng
2022-06-15 14:29 ` Sean Christopherson
2022-06-10 0:11 ` Marc Orr
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