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

[Mika Penttilä]

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?




> }
>   
>   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];
>   	};