From: Michael Roth <michael.roth@amd.com>
To: Chao Peng <chao.p.peng@linux.intel.com>
Cc: <kvm@vger.kernel.org>, <linux-kernel@vger.kernel.org>,
<linux-mm@kvack.org>, <linux-fsdevel@vger.kernel.org>,
<linux-arch@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>,
Sean Christopherson <seanjc@google.com>,
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@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>,
Shuah Khan <shuah@kernel.org>, Mike Rapoport <rppt@kernel.org>,
Steven Price <steven.price@arm.com>,
"Maciej S . Szmigiero" <mail@maciej.szmigiero.name>,
Vlastimil Babka <vbabka@suse.cz>,
Vishal Annapurve <vannapurve@google.com>,
Yu Zhang <yu.c.zhang@linux.intel.com>,
"Kirill A . Shutemov" <kirill.shutemov@linux.intel.com>,
<luto@kernel.org>, <jun.nakajima@intel.com>,
<dave.hansen@intel.com>, <ak@linux.intel.com>, <david@redhat.com>,
<aarcange@redhat.com>, <ddutile@redhat.com>,
<dhildenb@redhat.com>, Quentin Perret <qperret@google.com>,
<tabba@google.com>, <mhocko@suse.com>,
Muchun Song <songmuchun@bytedance.com>, <wei.w.wang@intel.com>
Subject: Re: [PATCH v9 1/8] mm: Introduce memfd_restricted system call to create restricted user memory
Date: Tue, 29 Nov 2022 13:18:15 -0600 [thread overview]
Message-ID: <20221129191815.atuv6arhodjbnvb2@amd.com> (raw)
In-Reply-To: <20221129190658.jefuep7nglp25ugt@amd.com>
On Tue, Nov 29, 2022 at 01:06:58PM -0600, Michael Roth wrote:
> On Tue, Nov 29, 2022 at 10:06:15PM +0800, Chao Peng wrote:
> > On Mon, Nov 28, 2022 at 06:37:25PM -0600, Michael Roth wrote:
> > > On Tue, Oct 25, 2022 at 11:13:37PM +0800, Chao Peng wrote:
> > ...
> > > > +static long restrictedmem_fallocate(struct file *file, int mode,
> > > > + loff_t offset, loff_t len)
> > > > +{
> > > > + struct restrictedmem_data *data = file->f_mapping->private_data;
> > > > + struct file *memfd = data->memfd;
> > > > + int ret;
> > > > +
> > > > + if (mode & FALLOC_FL_PUNCH_HOLE) {
> > > > + if (!PAGE_ALIGNED(offset) || !PAGE_ALIGNED(len))
> > > > + return -EINVAL;
> > > > + }
> > > > +
> > > > + restrictedmem_notifier_invalidate(data, offset, offset + len, true);
> > >
> > > The KVM restrictedmem ops seem to expect pgoff_t, but here we pass
> > > loff_t. For SNP we've made this strange as part of the following patch
> > > and it seems to produce the expected behavior:
> >
> > That's correct. Thanks.
> >
> > >
> > > https://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgithub.com%2Fmdroth%2Flinux%2Fcommit%2Fd669c7d3003ff7a7a47e73e8c3b4eeadbd2c4eb6&data=05%7C01%7CMichael.Roth%40amd.com%7C0c26815eb6af4f1a243508dad23cf713%7C3dd8961fe4884e608e11a82d994e183d%7C0%7C0%7C638053456609134623%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000%7C%7C%7C&sdata=kAL42bmyBB0alVwh%2FN%2BT3D%2BiVTdxxMsJ7V4TNuCTjM4%3D&reserved=0
> > >
> > > > + ret = memfd->f_op->fallocate(memfd, mode, offset, len);
> > > > + restrictedmem_notifier_invalidate(data, offset, offset + len, false);
> > > > + return ret;
> > > > +}
> > > > +
> > >
> > > <snip>
> > >
> > > > +int restrictedmem_get_page(struct file *file, pgoff_t offset,
> > > > + struct page **pagep, int *order)
> > > > +{
> > > > + struct restrictedmem_data *data = file->f_mapping->private_data;
> > > > + struct file *memfd = data->memfd;
> > > > + struct page *page;
> > > > + int ret;
> > > > +
> > > > + ret = shmem_getpage(file_inode(memfd), offset, &page, SGP_WRITE);
> > >
> > > This will result in KVM allocating pages that userspace hasn't necessary
> > > fallocate()'d. In the case of SNP we need to get the PFN so we can clean
> > > up the RMP entries when restrictedmem invalidations are issued for a GFN
> > > range.
> >
> > Yes fallocate() is unnecessary unless someone wants to reserve some
> > space (e.g. for determination or performance purpose), this matches its
> > semantics perfectly at:
> > https://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Fwww.man7.org%2Flinux%2Fman-pages%2Fman2%2Ffallocate.2.html&data=05%7C01%7CMichael.Roth%40amd.com%7C0c26815eb6af4f1a243508dad23cf713%7C3dd8961fe4884e608e11a82d994e183d%7C0%7C0%7C638053456609134623%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000%7C%7C%7C&sdata=acBSquFG%2FHtpbcZfHDZrP2O63bu06rI0pjiPJFSJSj8%3D&reserved=0
> >
> > >
> > > If the guest supports lazy-acceptance however, these pages may not have
> > > been faulted in yet, and if the VMM defers actually fallocate()'ing space
> > > until the guest actually tries to issue a shared->private for that GFN
> > > (to support lazy-pinning), then there may never be a need to allocate
> > > pages for these backends.
> > >
> > > However, the restrictedmem invalidations are for GFN ranges so there's
> > > no way to know inadvance whether it's been allocated yet or not. The
> > > xarray is one option but currently it defaults to 'private' so that
> > > doesn't help us here. It might if we introduced a 'uninitialized' state
> > > or something along that line instead of just the binary
> > > 'shared'/'private' though...
> >
> > How about if we change the default to 'shared' as we discussed at
> > https://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Flore.kernel.org%2Fall%2FY35gI0L8GMt9%2BOkK%40google.com%2F&data=05%7C01%7CMichael.Roth%40amd.com%7C0c26815eb6af4f1a243508dad23cf713%7C3dd8961fe4884e608e11a82d994e183d%7C0%7C0%7C638053456609134623%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000%7C%7C%7C&sdata=Q1vZWQiZ7mx12Qn5aKl4s8Ea9hNbwCJBb%2BjiA1du3Os%3D&reserved=0?
>
> Need to look at this a bit more, but I think that could work as well.
>
> > >
> > > But for now we added a restrictedmem_get_page_noalloc() that uses
> > > SGP_NONE instead of SGP_WRITE to avoid accidentally allocating a bunch
> > > of memory as part of guest shutdown, and a
> > > kvm_restrictedmem_get_pfn_noalloc() variant to go along with that. But
> > > maybe a boolean param is better? Or maybe SGP_NOALLOC is the better
> > > default, and we just propagate an error to userspace if they didn't
> > > fallocate() in advance?
> >
> > This (making fallocate() a hard requirement) not only complicates the
> > userspace but also forces the lazy-faulting going through a long path of
> > exiting to userspace. Unless we don't have other options I would not go
> > this way.
>
> Unless I'm missing something, it's already the case that userspace is
> responsible for handling all the shared->private transitions in response
> to KVM_EXIT_MEMORY_FAULT or (in our case) KVM_EXIT_VMGEXIT. So it only
> places the additional requirements on the VMM that if they *don't*
> preallocate, then they'll need to issue the fallocate() prior to issuing
> the KVM_MEM_ENCRYPT_REG_REGION ioctl in response to these events.
>
> QEMU for example already has a separate 'prealloc' option for cases
> where they want to prefault all the guest memory, so it makes sense to
> continue making that an optional thing with regard to UPM.
Although I guess what you're suggesting doesn't stop userspace from
deciding whether they want to prefault or not. I know the Google folks
had some concerns over unexpected allocations causing 2x memory usage
though so giving userspace full control of what is/isn't allocated in
the restrictedmem backend seems to make it easier to guard against this,
but I think checking the xarray and defaulting to 'shared' would work
for us if that's the direction we end up going.
-Mike
>
> -Mike
>
> >
> > Chao
> > >
> > > -Mike
> > >
> > > > + if (ret)
> > > > + return ret;
> > > > +
> > > > + *pagep = page;
> > > > + if (order)
> > > > + *order = thp_order(compound_head(page));
> > > > +
> > > > + SetPageUptodate(page);
> > > > + unlock_page(page);
> > > > +
> > > > + return 0;
> > > > +}
> > > > +EXPORT_SYMBOL_GPL(restrictedmem_get_page);
> > > > --
> > > > 2.25.1
> > > >
next prev parent reply other threads:[~2022-11-29 19:18 UTC|newest]
Thread overview: 101+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-10-25 15:13 [PATCH v9 0/8] KVM: mm: fd-based approach for supporting KVM Chao Peng
2022-10-25 15:13 ` [PATCH v9 1/8] mm: Introduce memfd_restricted system call to create restricted user memory Chao Peng
2022-10-26 17:31 ` Isaku Yamahata
2022-10-28 6:12 ` Chao Peng
2022-10-27 10:20 ` Fuad Tabba
2022-10-31 17:47 ` Michael Roth
2022-11-01 11:37 ` Chao Peng
2022-11-01 15:19 ` Michael Roth
2022-11-01 19:30 ` Michael Roth
2022-11-02 14:53 ` Chao Peng
2022-11-02 21:19 ` Michael Roth
2022-11-14 14:02 ` Vlastimil Babka
2022-11-14 15:28 ` Kirill A. Shutemov
2022-11-14 22:16 ` Michael Roth
2022-11-15 9:48 ` Chao Peng
2022-11-14 22:16 ` Michael Roth
2022-11-02 21:14 ` Kirill A. Shutemov
2022-11-02 21:26 ` Michael Roth
2022-11-02 22:07 ` Michael Roth
2022-11-03 16:30 ` Kirill A. Shutemov
2022-11-29 0:06 ` Michael Roth
2022-11-29 11:21 ` Kirill A. Shutemov
2022-11-29 11:39 ` David Hildenbrand
2022-11-29 13:59 ` Chao Peng
2022-11-29 13:58 ` Chao Peng
2022-11-29 0:37 ` Michael Roth
2022-11-29 14:06 ` Chao Peng
2022-11-29 19:06 ` Michael Roth
2022-11-29 19:18 ` Michael Roth [this message]
2022-11-30 9:39 ` Chao Peng
2022-11-30 14:31 ` Michael Roth
2022-11-29 18:01 ` Vishal Annapurve
2022-12-02 2:16 ` Vishal Annapurve
2022-12-02 6:49 ` Chao Peng
2022-12-02 13:44 ` Kirill A . Shutemov
2022-10-25 15:13 ` [PATCH v9 2/8] KVM: Extend the memslot to support fd-based private memory Chao Peng
2022-10-27 10:25 ` Fuad Tabba
2022-10-28 7:04 ` Xiaoyao Li
2022-10-31 14:14 ` Chao Peng
2022-11-14 16:04 ` Alex Bennée
2022-11-15 9:29 ` Chao Peng
2022-10-25 15:13 ` [PATCH v9 3/8] KVM: Add KVM_EXIT_MEMORY_FAULT exit Chao Peng
2022-10-25 15:26 ` Peter Maydell
2022-10-25 16:17 ` Sean Christopherson
2022-10-27 10:27 ` Fuad Tabba
2022-10-28 6:14 ` Chao Peng
2022-11-15 16:56 ` Alex Bennée
2022-11-16 3:14 ` Chao Peng
2022-11-16 19:03 ` Alex Bennée
2022-11-17 13:45 ` Chao Peng
2022-11-17 15:08 ` Alex Bennée
2022-11-18 1:32 ` Chao Peng
2022-11-18 13:23 ` Alex Bennée
2022-11-18 15:59 ` Sean Christopherson
2022-11-22 9:50 ` Chao Peng
2022-11-23 18:02 ` Sean Christopherson
2022-11-16 18:15 ` Andy Lutomirski
2022-11-16 18:48 ` Sean Christopherson
2022-11-17 13:42 ` Chao Peng
2022-10-25 15:13 ` [PATCH v9 4/8] KVM: Use gfn instead of hva for mmu_notifier_retry Chao Peng
2022-10-27 10:29 ` Fuad Tabba
2022-11-04 2:28 ` Chao Peng
2022-11-04 22:29 ` Sean Christopherson
2022-11-08 7:16 ` Chao Peng
2022-11-10 17:53 ` Sean Christopherson
2022-11-10 20:06 ` Sean Christopherson
2022-11-11 8:27 ` Chao Peng
2022-10-25 15:13 ` [PATCH v9 5/8] KVM: Register/unregister the guest private memory regions Chao Peng
2022-10-27 10:31 ` Fuad Tabba
2022-11-03 23:04 ` Sean Christopherson
2022-11-04 8:28 ` Chao Peng
2022-11-04 21:19 ` Sean Christopherson
2022-11-08 8:24 ` Chao Peng
2022-11-08 1:35 ` Yuan Yao
2022-11-08 9:41 ` Chao Peng
2022-11-09 5:52 ` Yuan Yao
2022-11-16 22:24 ` Sean Christopherson
2022-11-17 13:20 ` Chao Peng
2022-10-25 15:13 ` [PATCH v9 6/8] KVM: Update lpage info when private/shared memory are mixed Chao Peng
2022-10-26 20:46 ` Isaku Yamahata
2022-10-28 6:38 ` Chao Peng
2022-11-08 12:08 ` Yuan Yao
2022-11-09 4:13 ` Chao Peng
2022-10-25 15:13 ` [PATCH v9 7/8] KVM: Handle page fault for private memory Chao Peng
2022-10-26 21:54 ` Isaku Yamahata
2022-10-28 6:55 ` Chao Peng
2022-11-01 0:02 ` Isaku Yamahata
2022-11-01 11:38 ` Chao Peng
2022-11-16 20:50 ` Ackerley Tng
2022-11-16 22:13 ` Sean Christopherson
2022-11-17 13:25 ` Chao Peng
2022-10-25 15:13 ` [PATCH v9 8/8] KVM: Enable and expose KVM_MEM_PRIVATE Chao Peng
2022-10-27 10:31 ` Fuad Tabba
2022-11-03 12:13 ` [PATCH v9 0/8] KVM: mm: fd-based approach for supporting KVM Vishal Annapurve
2022-11-08 0:41 ` Isaku Yamahata
2022-11-09 15:54 ` Kirill A. Shutemov
2022-11-15 14:36 ` Kirill A. Shutemov
2022-11-14 11:43 ` Alex Bennée
2022-11-16 5:00 ` Chao Peng
2022-11-16 9:40 ` Alex Bennée
2022-11-17 14:16 ` Chao Peng
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