From: "Alex Bennée" <alex.bennee@linaro.org>
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,
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Subject: Re: [PATCH v9 3/8] KVM: Add KVM_EXIT_MEMORY_FAULT exit
Date: Thu, 17 Nov 2022 15:08:17 +0000 [thread overview]
Message-ID: <87a64p8vof.fsf@linaro.org> (raw)
In-Reply-To: <20221117134520.GD422408@chaop.bj.intel.com>
Chao Peng <chao.p.peng@linux.intel.com> writes:
> On Wed, Nov 16, 2022 at 07:03:49PM +0000, Alex Bennée wrote:
>>
>> Chao Peng <chao.p.peng@linux.intel.com> writes:
>>
>> > On Tue, Nov 15, 2022 at 04:56:12PM +0000, Alex Bennée wrote:
>> >>
>> >> Chao Peng <chao.p.peng@linux.intel.com> writes:
>> >>
>> >> > This new KVM exit allows userspace to handle memory-related errors. It
>> >> > indicates an error happens in KVM at guest memory range [gpa, gpa+size).
>> >> > The flags includes additional information for userspace to handle the
>> >> > error. Currently bit 0 is defined as 'private memory' where '1'
>> >> > indicates error happens due to private memory access and '0' indicates
>> >> > error happens due to shared memory access.
>> >> >
>> >> > When private memory is enabled, this new exit will be used for KVM to
>> >> > exit to userspace for shared <-> private memory conversion in memory
>> >> > encryption usage. In such usage, typically there are two kind of memory
>> >> > conversions:
>> >> > - explicit conversion: happens when guest explicitly calls into KVM
>> >> > to map a range (as private or shared), KVM then exits to userspace
>> >> > to perform the map/unmap operations.
>> >> > - implicit conversion: happens in KVM page fault handler where KVM
>> >> > exits to userspace for an implicit conversion when the page is in a
>> >> > different state than requested (private or shared).
>> >> >
>> >> > Suggested-by: Sean Christopherson <seanjc@google.com>
>> >> > Co-developed-by: Yu Zhang <yu.c.zhang@linux.intel.com>
>> >> > Signed-off-by: Yu Zhang <yu.c.zhang@linux.intel.com>
>> >> > Signed-off-by: Chao Peng <chao.p.peng@linux.intel.com>
>> >> > ---
>> >> > Documentation/virt/kvm/api.rst | 23 +++++++++++++++++++++++
>> >> > include/uapi/linux/kvm.h | 9 +++++++++
>> >> > 2 files changed, 32 insertions(+)
>> >> >
>> >> > diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst
>> >> > index f3fa75649a78..975688912b8c 100644
>> >> > --- a/Documentation/virt/kvm/api.rst
>> >> > +++ b/Documentation/virt/kvm/api.rst
>> >> > @@ -6537,6 +6537,29 @@ array field represents return values. The userspace should update the return
>> >> > values of SBI call before resuming the VCPU. For more details on RISC-V SBI
>> >> > spec refer, https://github.com/riscv/riscv-sbi-doc.
>> >> >
>> >> > +::
>> >> > +
>> >> > + /* KVM_EXIT_MEMORY_FAULT */
>> >> > + struct {
>> >> > + #define KVM_MEMORY_EXIT_FLAG_PRIVATE (1 << 0)
>> >> > + __u32 flags;
>> >> > + __u32 padding;
>> >> > + __u64 gpa;
>> >> > + __u64 size;
>> >> > + } memory;
>> >> > +
>> >> > +If exit reason is KVM_EXIT_MEMORY_FAULT then it indicates that the VCPU has
>> >> > +encountered a memory error which is not handled by KVM kernel module and
>> >> > +userspace may choose to handle it. The 'flags' field indicates the memory
>> >> > +properties of the exit.
>> >> > +
>> >> > + - KVM_MEMORY_EXIT_FLAG_PRIVATE - indicates the memory error is caused by
>> >> > + private memory access when the bit is set. Otherwise the memory error is
>> >> > + caused by shared memory access when the bit is clear.
>> >>
>> >> What does a shared memory access failure entail?
>> >
>> > In the context of confidential computing usages, guest can issue a
>> > shared memory access while the memory is actually private from the host
>> > point of view. This exit with bit 0 cleared gives userspace a chance to
>> > convert the private memory to shared memory on host.
>>
>> I think this should be explicit rather than implied by the absence of
>> another flag. Sean suggested you might want flags for RWX failures so
>> maybe something like:
>>
>> KVM_MEMORY_EXIT_SHARED_FLAG_READ (1 << 0)
>> KVM_MEMORY_EXIT_SHARED_FLAG_WRITE (1 << 1)
>> KVM_MEMORY_EXIT_SHARED_FLAG_EXECUTE (1 << 2)
>> KVM_MEMORY_EXIT_FLAG_PRIVATE (1 << 3)
>
> Yes, but I would not add 'SHARED' to RWX, they are not share memory
> specific, private memory can also set them once introduced.
OK so how about:
KVM_MEMORY_EXIT_FLAG_READ (1 << 0)
KVM_MEMORY_EXIT_FLAG_WRITE (1 << 1)
KVM_MEMORY_EXIT_FLAG_EXECUTE (1 << 2)
KVM_MEMORY_EXIT_FLAG_SHARED (1 << 3)
KVM_MEMORY_EXIT_FLAG_PRIVATE (1 << 4)
>
> Thanks,
> Chao
>>
>> which would allow you to signal the various failure modes of the shared
>> region, or that you had accessed private memory.
>>
>> >
>> >>
>> >> If you envision any other failure modes it might be worth making it
>> >> explicit with additional flags.
>> >
>> > Sean mentioned some more usages[1][]2] other than the memory conversion
>> > for confidential usage. But I would leave those flags being added in the
>> > future after those usages being well discussed.
>> >
>> > [1] https://lkml.kernel.org/r/20200617230052.GB27751@linux.intel.com
>> > [2] https://lore.kernel.org/all/YKxJLcg%2FWomPE422@google.com
>> >
>> >> I also wonder if a bitmask makes sense if
>> >> there can only be one reason for a failure? Maybe all that is needed is
>> >> a reason enum?
>> >
>> > Tough we only have one reason right now but we still want to leave room
>> > for future extension. Enum can express a single value at once well but
>> > bitmask makes it possible to express multiple orthogonal flags.
>>
>> I agree if multiple orthogonal failures can occur at once a bitmask is
>> the right choice.
>>
>> >
>> > Chao
>> >>
>> >> > +
>> >> > +'gpa' and 'size' indicate the memory range the error occurs at. The userspace
>> >> > +may handle the error and return to KVM to retry the previous memory access.
>> >> > +
>> >> > ::
>> >> >
>> >> > /* KVM_EXIT_NOTIFY */
>> >> > diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
>> >> > index f1ae45c10c94..fa60b032a405 100644
>> >> > --- a/include/uapi/linux/kvm.h
>> >> > +++ b/include/uapi/linux/kvm.h
>> >> > @@ -300,6 +300,7 @@ struct kvm_xen_exit {
>> >> > #define KVM_EXIT_RISCV_SBI 35
>> >> > #define KVM_EXIT_RISCV_CSR 36
>> >> > #define KVM_EXIT_NOTIFY 37
>> >> > +#define KVM_EXIT_MEMORY_FAULT 38
>> >> >
>> >> > /* For KVM_EXIT_INTERNAL_ERROR */
>> >> > /* Emulate instruction failed. */
>> >> > @@ -538,6 +539,14 @@ struct kvm_run {
>> >> > #define KVM_NOTIFY_CONTEXT_INVALID (1 << 0)
>> >> > __u32 flags;
>> >> > } notify;
>> >> > + /* KVM_EXIT_MEMORY_FAULT */
>> >> > + struct {
>> >> > +#define KVM_MEMORY_EXIT_FLAG_PRIVATE (1 << 0)
>> >> > + __u32 flags;
>> >> > + __u32 padding;
>> >> > + __u64 gpa;
>> >> > + __u64 size;
>> >> > + } memory;
>> >> > /* Fix the size of the union. */
>> >> > char padding[256];
>> >> > };
>> >>
>> >>
>> >> --
>> >> Alex Bennée
>>
>>
>> --
>> Alex Bennée
--
Alex Bennée
next prev parent reply other threads:[~2022-11-17 15:09 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
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 [this message]
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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