Re: [PATCH V3 2/2] KVM: PPC: Implement H_SVM_INIT_ABORT hcall

[Ram Pai <linuxram@us.ibm.com>]

On Sat, Dec 14, 2019 at 06:12:08PM -0800, Sukadev Bhattiprolu wrote:
> 
> Implement the H_SVM_INIT_ABORT hcall which the Ultravisor can use to
> abort an SVM after it has issued the H_SVM_INIT_START and before the
> H_SVM_INIT_DONE hcalls. This hcall could be used when Ultravisor
> encounters security violations or other errors when starting an SVM.
> 
> Note that this hcall is different from UV_SVM_TERMINATE ucall which
> is used by HV to terminate/cleanup an VM that has becore secure.
> 
> The H_SVM_INIT_ABORT should basically undo operations that were done
> since the H_SVM_INIT_START hcall - i.e page-out all the VM pages back
> to normal memory, and terminate the SVM.
> 
> (If we do not bring the pages back to normal memory, the text/data
> of the VM would be stuck in secure memory and since the SVM did not
> go secure, its MSR_S bit will be clear and the VM wont be able to
> access its pages even to do a clean exit).
> 
> Based on patches and discussion with Paul Mackerras, Ram Pai and
> Bharata Rao.
> 
> Signed-off-by: Ram Pai <linuxram@linux.ibm.com>
> Signed-off-by: Sukadev Bhattiprolu <sukadev@linux.ibm.com>
> Signed-off-by: Bharata B Rao <bharata@linux.ibm.com>
> ---
> Changelog[v3]:
> 	- Rather than pass the NIP/MSR as parameters, load them into
> 	  SRR0/SRR1 (like we do with other registers) and terminate
> 	  the VM after paging out pages
> 	- Move the code to add a skip_page_out parameter into a
> 	  separate patch.
> 
> Changelog[v2]:
> 	[Paul Mackerras] avoid returning to UV "one last time" after
> 	the state is cleaned up.  So, we now have H_SVM_INIT_ABORT:
> 	- take the VM's NIP/MSR register states as parameters
> 	- inherit the state of other registers as at UV_ESM call.
> 	After cleaning up the partial state, HV uses these to return
> 	directly to the VM with a failed UV_ESM call.
> ---
>  Documentation/powerpc/ultravisor.rst        | 57 +++++++++++++++++++++
>  arch/powerpc/include/asm/hvcall.h           |  1 +
>  arch/powerpc/include/asm/kvm_book3s_uvmem.h |  6 +++
>  arch/powerpc/include/asm/kvm_host.h         |  1 +
>  arch/powerpc/kvm/book3s_hv.c                |  3 ++
>  arch/powerpc/kvm/book3s_hv_uvmem.c          | 24 +++++++++
>  6 files changed, 92 insertions(+)
> 
> diff --git a/Documentation/powerpc/ultravisor.rst b/Documentation/powerpc/ultravisor.rst
> index 730854f73830..8c114c071bfa 100644
> --- a/Documentation/powerpc/ultravisor.rst
> +++ b/Documentation/powerpc/ultravisor.rst
> @@ -948,6 +948,63 @@ Use cases
>      up its internal state for this virtual machine.
> 
> 
> +H_SVM_INIT_ABORT
> +----------------
> +
> +    Abort the process of securing an SVM.
> +
> +Syntax
> +~~~~~~
> +
> +.. code-block:: c
> +
> +	uint64_t hypercall(const uint64_t H_SVM_INIT_ABORT)
> +
> +Return values
> +~~~~~~~~~~~~~
> +
> +    One of the following values:
> +
> +	* H_PARAMETER 		on successfully cleaning up the state,
> +				Hypervisor will return this value to the
> +				**guest**, to indicate that the underlying
> +				UV_ESM ultracall failed.
> +
> +	* H_UNSUPPORTED		if called from the wrong context (e.g. from
> +				an SVM or before an H_SVM_INIT_START hypercall).
> +
> +Description
> +~~~~~~~~~~~
> +
> +    Abort the process of securing a virtual machine. This call must
> +    be made after a prior call to ``H_SVM_INIT_START`` hypercall and
> +    before a call to ``H_SVM_INIT_DONE``.
> +
> +    On entry into this hypercall the non-volatile GPRs and FPRs are
> +    expected to contain the values they had at the time the VM issued
> +    the UV_ESM ultracall. Further ``SRR0`` is expected to contain the
> +    address of the instruction after the ``UV_ESM`` ultracall and ``SRR1``
> +    the MSR value with which to return to the VM.
> +
> +    This hypercall will cleanup any partial state that was established for
> +    the VM since the prior ``H_SVM_INIT_START`` hypercall, including paging
> +    out pages that were paged-into secure memory, and issue the
> +    ``UV_SVM_TERMINATE`` ultracall to terminate the VM.
> +
> +    After the partial state is cleaned up, control returns to the VM
> +    (**not Ultravisor**), at the address specified in ``SRR0`` with the
> +    MSR values set to the value in ``SRR1``.
> +
> +Use cases
> +~~~~~~~~~
> +
> +    If after a successful call to ``H_SVM_INIT_START``, the Ultravisor
> +    encounters an error while securing a virtual machine, either due
> +    to lack of resources or because the VM's security information could
> +    not be validated, Ultravisor informs the Hypervisor about it.
> +    Hypervisor should use this call to clean up any internal state for
> +    this virtual machine and return to the VM.
> +
>  H_SVM_PAGE_IN
>  -------------
> 
> diff --git a/arch/powerpc/include/asm/hvcall.h b/arch/powerpc/include/asm/hvcall.h
> index 13bd870609c3..e90c073e437e 100644
> --- a/arch/powerpc/include/asm/hvcall.h
> +++ b/arch/powerpc/include/asm/hvcall.h
> @@ -350,6 +350,7 @@
>  #define H_SVM_PAGE_OUT		0xEF04
>  #define H_SVM_INIT_START	0xEF08
>  #define H_SVM_INIT_DONE		0xEF0C
> +#define H_SVM_INIT_ABORT	0xEF14
> 
>  /* Values for 2nd argument to H_SET_MODE */
>  #define H_SET_MODE_RESOURCE_SET_CIABR		1
> diff --git a/arch/powerpc/include/asm/kvm_book3s_uvmem.h b/arch/powerpc/include/asm/kvm_book3s_uvmem.h
> index 3cf8425b9838..5a9834e0e2d1 100644
> --- a/arch/powerpc/include/asm/kvm_book3s_uvmem.h
> +++ b/arch/powerpc/include/asm/kvm_book3s_uvmem.h
> @@ -19,6 +19,7 @@ unsigned long kvmppc_h_svm_page_out(struct kvm *kvm,
>  unsigned long kvmppc_h_svm_init_start(struct kvm *kvm);
>  unsigned long kvmppc_h_svm_init_done(struct kvm *kvm);
>  int kvmppc_send_page_to_uv(struct kvm *kvm, unsigned long gfn);
> +unsigned long kvmppc_h_svm_init_abort(struct kvm *kvm);
>  void kvmppc_uvmem_drop_pages(const struct kvm_memory_slot *free,
>  			     struct kvm *kvm, bool skip_page_out);
>  #else
> @@ -62,6 +63,11 @@ static inline unsigned long kvmppc_h_svm_init_done(struct kvm *kvm)
>  	return H_UNSUPPORTED;
>  }
> 
> +static inline unsigned long kvmppc_h_svm_init_abort(struct kvm *kvm)
> +{
> +	return H_UNSUPPORTED;
> +}
> +
>  static inline int kvmppc_send_page_to_uv(struct kvm *kvm, unsigned long gfn)
>  {
>  	return -EFAULT;
> diff --git a/arch/powerpc/include/asm/kvm_host.h b/arch/powerpc/include/asm/kvm_host.h
> index 577ca95fac7c..8310c0407383 100644
> --- a/arch/powerpc/include/asm/kvm_host.h
> +++ b/arch/powerpc/include/asm/kvm_host.h
> @@ -278,6 +278,7 @@ struct kvm_resize_hpt;
>  /* Flag values for kvm_arch.secure_guest */
>  #define KVMPPC_SECURE_INIT_START 0x1 /* H_SVM_INIT_START has been called */
>  #define KVMPPC_SECURE_INIT_DONE  0x2 /* H_SVM_INIT_DONE completed */
> +#define KVMPPC_SECURE_INIT_ABORT 0x4 /* H_SVM_INIT_ABORT issued */
> 
>  struct kvm_arch {
>  	unsigned int lpid;
> diff --git a/arch/powerpc/kvm/book3s_hv.c b/arch/powerpc/kvm/book3s_hv.c
> index 66d5312be16b..1b22f2c7ad1b 100644
> --- a/arch/powerpc/kvm/book3s_hv.c
> +++ b/arch/powerpc/kvm/book3s_hv.c
> @@ -1099,6 +1099,9 @@ int kvmppc_pseries_do_hcall(struct kvm_vcpu *vcpu)
>  	case H_SVM_INIT_DONE:
>  		ret = kvmppc_h_svm_init_done(vcpu->kvm);
>  		break;
> +	case H_SVM_INIT_ABORT:
> +		ret = kvmppc_h_svm_init_abort(vcpu->kvm);
> +		break;
> 
>  	default:
>  		return RESUME_HOST;
> diff --git a/arch/powerpc/kvm/book3s_hv_uvmem.c b/arch/powerpc/kvm/book3s_hv_uvmem.c
> index 9a5bbad7d87e..f7df8c327468 100644
> --- a/arch/powerpc/kvm/book3s_hv_uvmem.c
> +++ b/arch/powerpc/kvm/book3s_hv_uvmem.c
> @@ -287,6 +287,30 @@ void kvmppc_uvmem_drop_pages(const struct kvm_memory_slot *free,
>  	}
>  }
> 
> +unsigned long kvmppc_h_svm_init_abort(struct kvm *kvm)
> +{
> +	int i;
> +
> +	if (!(kvm->arch.secure_guest & KVMPPC_SECURE_INIT_START))
> +		return H_UNSUPPORTED;

It should also return H_UNSUPPORTED when 
(kvm->arch.secure_guest & KVMPPC_SECURE_INIT_DONE) is true.

RP