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Message-ID: <20230720190211.GF25699@ls.amr.corp.intel.com>
Date: Thu, 20 Jul 2023 12:02:11 -0700
From: Isaku Yamahata <isaku.yamahata@...il.com>
To: Yuan Yao <yuan.yao@...ux.intel.com>
Cc: Sean Christopherson <seanjc@...gle.com>,
Paolo Bonzini <pbonzini@...hat.com>,
Marc Zyngier <maz@...nel.org>,
Oliver Upton <oliver.upton@...ux.dev>,
Huacai Chen <chenhuacai@...nel.org>,
Michael Ellerman <mpe@...erman.id.au>,
Anup Patel <anup@...infault.org>,
Paul Walmsley <paul.walmsley@...ive.com>,
Palmer Dabbelt <palmer@...belt.com>,
Albert Ou <aou@...s.berkeley.edu>,
"Matthew Wilcox (Oracle)" <willy@...radead.org>,
Andrew Morton <akpm@...ux-foundation.org>,
Paul Moore <paul@...l-moore.com>,
James Morris <jmorris@...ei.org>,
"Serge E. Hallyn" <serge@...lyn.com>, kvm@...r.kernel.org,
linux-arm-kernel@...ts.infradead.org, kvmarm@...ts.linux.dev,
linux-mips@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
kvm-riscv@...ts.infradead.org, linux-riscv@...ts.infradead.org,
linux-fsdevel@...r.kernel.org, linux-mm@...ck.org,
linux-security-module@...r.kernel.org,
linux-kernel@...r.kernel.org,
Chao Peng <chao.p.peng@...ux.intel.com>,
Fuad Tabba <tabba@...gle.com>,
Jarkko Sakkinen <jarkko@...nel.org>,
Yu Zhang <yu.c.zhang@...ux.intel.com>,
Vishal Annapurve <vannapurve@...gle.com>,
Ackerley Tng <ackerleytng@...gle.com>,
Maciej Szmigiero <mail@...iej.szmigiero.name>,
Vlastimil Babka <vbabka@...e.cz>,
David Hildenbrand <david@...hat.com>,
Quentin Perret <qperret@...gle.com>,
Michael Roth <michael.roth@....com>,
Wang <wei.w.wang@...el.com>,
Liam Merwick <liam.merwick@...cle.com>,
Isaku Yamahata <isaku.yamahata@...il.com>,
"Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>
Subject: Re: [RFC PATCH v11 08/29] KVM: Introduce per-page memory attributes
On Thu, Jul 20, 2023 at 04:09:12PM +0800,
Yuan Yao <yuan.yao@...ux.intel.com> wrote:
> On Tue, Jul 18, 2023 at 04:44:51PM -0700, Sean Christopherson wrote:
> > From: Chao Peng <chao.p.peng@...ux.intel.com>
> >
> > In confidential computing usages, whether a page is private or shared is
> > necessary information for KVM to perform operations like page fault
> > handling, page zapping etc. There are other potential use cases for
> > per-page memory attributes, e.g. to make memory read-only (or no-exec,
> > or exec-only, etc.) without having to modify memslots.
> >
> > Introduce two ioctls (advertised by KVM_CAP_MEMORY_ATTRIBUTES) to allow
> > userspace to operate on the per-page memory attributes.
> > - KVM_SET_MEMORY_ATTRIBUTES to set the per-page memory attributes to
> > a guest memory range.
> > - KVM_GET_SUPPORTED_MEMORY_ATTRIBUTES to return the KVM supported
> > memory attributes.
> >
> > Use an xarray to store the per-page attributes internally, with a naive,
> > not fully optimized implementation, i.e. prioritize correctness over
> > performance for the initial implementation.
> >
> > Because setting memory attributes is roughly analogous to mprotect() on
> > memory that is mapped into the guest, zap existing mappings prior to
> > updating the memory attributes. Opportunistically provide an arch hook
> > for the post-set path (needed to complete invalidation anyways) in
> > anticipation of x86 needing the hook to update metadata related to
> > determining whether or not a given gfn can be backed with various sizes
> > of hugepages.
> >
> > It's possible that future usages may not require an invalidation, e.g.
> > if KVM ends up supporting RWX protections and userspace grants _more_
> > protections, but again opt for simplicity and punt optimizations to
> > if/when they are needed.
> >
> > Suggested-by: Sean Christopherson <seanjc@...gle.com>
> > Link: https://lore.kernel.org/all/Y2WB48kD0J4VGynX@google.com
> > Cc: Fuad Tabba <tabba@...gle.com>
> > Signed-off-by: Chao Peng <chao.p.peng@...ux.intel.com>
> > Co-developed-by: Sean Christopherson <seanjc@...gle.com>
> > Signed-off-by: Sean Christopherson <seanjc@...gle.com>
> > ---
> > Documentation/virt/kvm/api.rst | 60 ++++++++++++
> > include/linux/kvm_host.h | 14 +++
> > include/uapi/linux/kvm.h | 14 +++
> > virt/kvm/Kconfig | 4 +
> > virt/kvm/kvm_main.c | 170 +++++++++++++++++++++++++++++++++
> > 5 files changed, 262 insertions(+)
> >
> > diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst
> > index 34d4ce66e0c8..0ca8561775ac 100644
> > --- a/Documentation/virt/kvm/api.rst
> > +++ b/Documentation/virt/kvm/api.rst
> > @@ -6068,6 +6068,56 @@ writes to the CNTVCT_EL0 and CNTPCT_EL0 registers using the SET_ONE_REG
> > interface. No error will be returned, but the resulting offset will not be
> > applied.
> >
> > +4.139 KVM_GET_SUPPORTED_MEMORY_ATTRIBUTES
> > +-----------------------------------------
> > +
> > +:Capability: KVM_CAP_MEMORY_ATTRIBUTES
> > +:Architectures: x86
> > +:Type: vm ioctl
> > +:Parameters: u64 memory attributes bitmask(out)
> > +:Returns: 0 on success, <0 on error
> > +
> > +Returns supported memory attributes bitmask. Supported memory attributes will
> > +have the corresponding bits set in u64 memory attributes bitmask.
> > +
> > +The following memory attributes are defined::
> > +
> > + #define KVM_MEMORY_ATTRIBUTE_PRIVATE (1ULL << 3)
> > +
> > +4.140 KVM_SET_MEMORY_ATTRIBUTES
> > +-----------------------------------------
> > +
> > +:Capability: KVM_CAP_MEMORY_ATTRIBUTES
> > +:Architectures: x86
> > +:Type: vm ioctl
> > +:Parameters: struct kvm_memory_attributes(in/out)
> > +:Returns: 0 on success, <0 on error
> > +
> > +Sets memory attributes for pages in a guest memory range. Parameters are
> > +specified via the following structure::
> > +
> > + struct kvm_memory_attributes {
> > + __u64 address;
> > + __u64 size;
> > + __u64 attributes;
> > + __u64 flags;
> > + };
> > +
> > +The user sets the per-page memory attributes to a guest memory range indicated
> > +by address/size, and in return KVM adjusts address and size to reflect the
> > +actual pages of the memory range have been successfully set to the attributes.
> > +If the call returns 0, "address" is updated to the last successful address + 1
> > +and "size" is updated to the remaining address size that has not been set
> > +successfully. The user should check the return value as well as the size to
> > +decide if the operation succeeded for the whole range or not. The user may want
> > +to retry the operation with the returned address/size if the previous range was
> > +partially successful.
> > +
> > +Both address and size should be page aligned and the supported attributes can be
> > +retrieved with KVM_GET_SUPPORTED_MEMORY_ATTRIBUTES.
> > +
> > +The "flags" field may be used for future extensions and should be set to 0s.
> > +
> > 5. The kvm_run structure
> > ========================
> >
> > @@ -8494,6 +8544,16 @@ block sizes is exposed in KVM_CAP_ARM_SUPPORTED_BLOCK_SIZES as a
> > 64-bit bitmap (each bit describing a block size). The default value is
> > 0, to disable the eager page splitting.
> >
> > +8.41 KVM_CAP_MEMORY_ATTRIBUTES
> > +------------------------------
> > +
> > +:Capability: KVM_CAP_MEMORY_ATTRIBUTES
> > +:Architectures: x86
> > +:Type: vm
> > +
> > +This capability indicates KVM supports per-page memory attributes and ioctls
> > +KVM_GET_SUPPORTED_MEMORY_ATTRIBUTES/KVM_SET_MEMORY_ATTRIBUTES are available.
> > +
> > 9. Known KVM API problems
> > =========================
> >
> > diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
> > index e9ca49d451f3..97db63da6227 100644
> > --- a/include/linux/kvm_host.h
> > +++ b/include/linux/kvm_host.h
> > @@ -264,6 +264,7 @@ struct kvm_gfn_range {
> > gfn_t end;
> > union {
> > pte_t pte;
> > + unsigned long attributes;
> > u64 raw;
> > } arg;
> > bool may_block;
> > @@ -809,6 +810,9 @@ struct kvm {
> >
> > #ifdef CONFIG_HAVE_KVM_PM_NOTIFIER
> > struct notifier_block pm_notifier;
> > +#endif
> > +#ifdef CONFIG_KVM_GENERIC_MEMORY_ATTRIBUTES
> > + struct xarray mem_attr_array;
> > #endif
> > char stats_id[KVM_STATS_NAME_SIZE];
> > };
> > @@ -2301,4 +2305,14 @@ static inline void kvm_account_pgtable_pages(void *virt, int nr)
> > /* Max number of entries allowed for each kvm dirty ring */
> > #define KVM_DIRTY_RING_MAX_ENTRIES 65536
> >
> > +#ifdef CONFIG_KVM_GENERIC_MEMORY_ATTRIBUTES
> > +static inline unsigned long kvm_get_memory_attributes(struct kvm *kvm, gfn_t gfn)
> > +{
> > + return xa_to_value(xa_load(&kvm->mem_attr_array, gfn));
> > +}
> > +
> > +bool kvm_arch_post_set_memory_attributes(struct kvm *kvm,
> > + struct kvm_gfn_range *range);
>
> Used but no definition in this patch, it's defined in next patch 09.
> How about add weak version in this patch and let ARCHs to overide it ?
It is guarded by CONFIG_KVM_GENERIC_MEMORY_ATTRIBUTES.
--
Isaku Yamahata <isaku.yamahata@...il.com>
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