Re: [PATCH v5 07/13] KVM: Add KVM_EXIT_MEMORY_ERROR exit

[Chao Peng <chao.p.peng@linux.intel.com>]

On Mon, Mar 28, 2022 at 10:33:37PM +0000, Sean Christopherson wrote:
> On Thu, Mar 10, 2022, Chao Peng 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.
> > 
> > After private memory is enabled, this new exit will be used for KVM to
> > exit to userspace for shared memory <-> 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
> >     do the map/unmap operations.
> >   - implicit conversion: happens in KVM page fault handler.
> >     * if the fault is due to a private memory access then causes a
> >       userspace exit for a shared->private conversion request when the
> >       page has not been allocated in the private memory backend.
> >     * If the fault is due to a shared memory access then causes a
> >       userspace exit for a private->shared conversion request when the
> >       page has already been allocated in the private memory backend.
> > 
> > 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 | 22 ++++++++++++++++++++++
> >  include/uapi/linux/kvm.h       |  9 +++++++++
> >  2 files changed, 31 insertions(+)
> > 
> > diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst
> > index f76ac598606c..bad550c2212b 100644
> > --- a/Documentation/virt/kvm/api.rst
> > +++ b/Documentation/virt/kvm/api.rst
> > @@ -6216,6 +6216,28 @@ 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_ERROR */
> > +		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_ERROR then it indicates that the VCPU has
> 
> Doh, I'm pretty sure I suggested KVM_EXIT_MEMORY_ERROR.  Any objection to using
> KVM_EXIT_MEMORY_FAULT instead of KVM_EXIT_MEMORY_ERROR?  "ERROR" makes me think
> of ECC errors, i.e. uncorrected #MC in x86 land, not more generic "faults".  That
> would align nicely with -EFAULT.

Sure.

> 
> > +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.