Re: [PATCH v10 4/9] KVM: Add KVM_EXIT_MEMORY_FAULT exit

Chao Peng
2022-12-07T15:16:38Z

On Tue, Dec 06, 2022 at 03:47:20PM +0000, Fuad Tabba wrote:
> Hi,
>
> On Fri, Dec 2, 2022 at 6:19 AM Chao Peng <chao.p.peng@linux.intel.com> wrote:
> >
> > 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>
> > Reviewed-by: Fuad Tabba <tabba@google.com>
> > ---
> > Documentation/virt/kvm/api.rst | 22 ++++++++++++++++++++++
> > include/uapi/linux/kvm.h | 8 ++++++++
> > 2 files changed, 30 insertions(+)
> >
> > diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst
> > index 99352170c130..d9edb14ce30b 100644
> > --- a/Documentation/virt/kvm/api.rst
> > +++ b/Documentation/virt/kvm/api.rst
> > @@ -6634,6 +6634,28 @@ 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 (1ULL << 0)
> > + __u64 flags;
>
> I see you've removed the padding and increased the flag size.

Yes Sean suggested this and also looks good to me.

Chao
>
> Reviewed-by: Fuad Tabba <tabba@google.com>
> Tested-by: Fuad Tabba <tabba@google.com>
>
> Cheers,
> /fuad
>
>
>
>
> > + __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.
> > +
> > +'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 13bff963b8b0..c7e9d375a902 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. */
> > @@ -541,6 +542,13 @@ struct kvm_run {
> > #define KVM_NOTIFY_CONTEXT_INVALID (1 << 0)
> > __u32 flags;
> > } notify;
> > + /* KVM_EXIT_MEMORY_FAULT */
> > + struct {
> > +#define KVM_MEMORY_EXIT_FLAG_PRIVATE (1ULL << 0)
> > + __u64 flags;
> > + __u64 gpa;
> > + __u64 size;
> > + } memory;
> > /* Fix the size of the union. */
> > char padding[256];
> > };
> > --
> > 2.25.1
> >