Re: [RFC PATCH 5/6] kvm: x86: add KVM_EXIT_MEMORY_ERROR exit

[Chao Peng]

On Thu, Nov 11, 2021 at 05:08:47PM +0200, Mika Penttilä wrote:
> 
> 
> On 11.11.2021 16.13, Chao Peng wrote:
> > Currently support to exit to userspace for private/shared memory
> > conversion.
> > 
> > Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx>
> > Signed-off-by: Yu Zhang <yu.c.zhang@xxxxxxxxxxxxxxx>
> > Signed-off-by: Chao Peng <chao.p.peng@xxxxxxxxxxxxxxx>
> > ---
> >   arch/x86/kvm/mmu/mmu.c   | 20 ++++++++++++++++++++
> >   include/uapi/linux/kvm.h | 15 +++++++++++++++
> >   2 files changed, 35 insertions(+)
> > 
> > diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
> > index af5ecf4ef62a..780868888aa8 100644
> > --- a/arch/x86/kvm/mmu/mmu.c
> > +++ b/arch/x86/kvm/mmu/mmu.c
> > @@ -3950,6 +3950,17 @@ static bool try_async_pf(struct kvm_vcpu *vcpu, bool prefault, gfn_t gfn,
> >   	slot = __kvm_vcpu_gfn_to_memslot(vcpu, gfn, private);
> > +	/*
> > +	 * Exit to userspace to map the requested private/shared memory region
> > +	 * if there is no memslot and (a) the access is private or (b) there is
> > +	 * an existing private memslot.  Emulated MMIO must be accessed through
> > +	 * shared GPAs, thus a memslot miss on a private GPA is always handled
> > +	 * as an implicit conversion "request".
> > +	 */
> > +	if (!slot &&
> > +	    (private || __kvm_vcpu_gfn_to_memslot(vcpu, gfn, true)))
> > +		goto out_convert;
> > +
> >   	/* Don't expose aliases for no slot GFNs or private memslots */
> >   	if ((cr2_or_gpa & vcpu_gpa_stolen_mask(vcpu)) &&
> >   	    !kvm_is_visible_memslot(slot)) {
> > @@ -3994,6 +4005,15 @@ static bool try_async_pf(struct kvm_vcpu *vcpu, bool prefault, gfn_t gfn,
> >   	*pfn = __gfn_to_pfn_memslot(slot, gfn, false, NULL,
> >   				    write, writable, hva);
> >   	return false;
> > +
> > +out_convert:
> > +	vcpu->run->exit_reason = KVM_EXIT_MEMORY_ERROR;
> > +	vcpu->run->mem.type = private ? KVM_EXIT_MEM_MAP_PRIVATE
> > +				      : KVM_EXIT_MEM_MAP_SHARE;
> > +	vcpu->run->mem.u.map.gpa = cr2_or_gpa;
> > +	vcpu->run->mem.u.map.size = PAGE_SIZE;
> > +	return true;
> > +
> I think this does just retry, no exit to user space?

Good catch, thanks.
Chao
> 
> 
> 
> 
> > }
> >   static int direct_page_fault(struct kvm_vcpu *vcpu, gpa_t gpa, u32 error_code,
> > diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
> > index 8d20caae9180..470c472a9451 100644
> > --- a/include/uapi/linux/kvm.h
> > +++ b/include/uapi/linux/kvm.h
> > @@ -233,6 +233,18 @@ struct kvm_xen_exit {
> >   	} u;
> >   };
> > +struct kvm_memory_exit {
> > +#define KVM_EXIT_MEM_MAP_SHARE          1
> > +#define KVM_EXIT_MEM_MAP_PRIVATE        2
> > +	__u32 type;
> > +	union {
> > +		struct {
> > +			__u64 gpa;
> > +			__u64 size;
> > +		} map;
> > +	} u;
> > +};
> > +
> >   #define KVM_S390_GET_SKEYS_NONE   1
> >   #define KVM_S390_SKEYS_MAX        1048576
> > @@ -272,6 +284,7 @@ struct kvm_xen_exit {
> >   #define KVM_EXIT_X86_BUS_LOCK     33
> >   #define KVM_EXIT_XEN              34
> >   #define KVM_EXIT_TDVMCALL         35
> > +#define KVM_EXIT_MEMORY_ERROR	  36
> >   /* For KVM_EXIT_INTERNAL_ERROR */
> >   /* Emulate instruction failed. */
> > @@ -455,6 +468,8 @@ struct kvm_run {
> >   			__u64 subfunc;
> >   			__u64 param[4];
> >   		} tdvmcall;
> > +		/* KVM_EXIT_MEMORY_ERROR */
> > +		struct kvm_memory_exit mem;
> >   		/* Fix the size of the union. */
> >   		char padding[256];
> >   	};
>