Subject: Re: [PATCH v4 2/2] KVM: PPC: Implement H_SVM_INIT_ABORT hcall

From: Sukadev Bhattiprolu <[email-masked]>
Date: Mon, 6 Jan 2020 18:02:37 -0800

Ram Pai [[email-masked]] wrote:
>
> One small comment.. H_STATE is a better return code than H_UNSUPPORTED.
> 

Here is the updated patch - we now return H_STATE if the abort call is
made after the VM has gone secure.
---
>From 73fe1fa5aff2829f2fae6a339169e56dc0bbae06 Mon Sep 17 00:00:00 2001
From: Sukadev Bhattiprolu <[email-masked]>
Date: Fri, 27 Sep 2019 14:30:36 -0500
Subject: [PATCH 2/2] KVM: PPC: Implement H_SVM_INIT_ABORT hcall

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 <[email-masked]>
Signed-off-by: Sukadev Bhattiprolu <[email-masked]>
Signed-off-by: Bharata B Rao <[email-masked]>
---
Changelog[v4]:
	- [Bharata Rao] Add missing rcu locking
	- [Paul Mackerras] simplify code that walks memslots
	- Add a check to ensure that H_SVM_INIT_ABORT is called before
	  H_SVM_INIT_DONE hcall (i.e the SVM is not already secure).
	- [Ram Pai] Return H_STATE if hcall is called after *INIT_DONE.

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        | 60 +++++++++++++++++++++
 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          | 28 ++++++++++
 6 files changed, 99 insertions(+)

diff --git a/Documentation/powerpc/ultravisor.rst b/Documentation/powerpc/ultravisor.rst
index 730854f73830..363736d7fd36 100644
--- a/Documentation/powerpc/ultravisor.rst
+++ b/Documentation/powerpc/ultravisor.rst
@@ -948,6 +948,66 @@ 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_STATE		if called after a VM has gone secure (i.e
+				H_SVM_INIT_DONE hypercall was successful).
+
+	* H_UNSUPPORTED		if called from a wrong context (e.g. from a
+				normal VM).
+
+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..522b57be0d45 100644
--- a/arch/powerpc/kvm/book3s_hv_uvmem.c
+++ b/arch/powerpc/kvm/book3s_hv_uvmem.c
@@ -287,6 +287,34 @@ void kvmppc_uvmem_drop_pages(const struct kvm_memory_slot *free,
 	}
 }
 
+unsigned long kvmppc_h_svm_init_abort(struct kvm *kvm)
+{
+	int srcu_idx;
+	struct kvm_memory_slot *memslot;
+
+	/*
+	 * Expect to be called only after INIT_START and before INIT_DONE.
+	 * If INIT_DONE was completed, use normal VM termination sequence.
+	 */
+	if (!(kvm->arch.secure_guest & KVMPPC_SECURE_INIT_START))
+		return H_UNSUPPORTED;
+
+	if (kvm->arch.secure_guest & KVMPPC_SECURE_INIT_DONE)
+		return H_STATE;
+
+	srcu_idx = srcu_read_lock(&kvm->srcu);
+
+	kvm_for_each_memslot(memslot, kvm_memslots(kvm))
+		kvmppc_uvmem_drop_pages(memslot, kvm, false);
+
+	srcu_read_unlock(&kvm->srcu, srcu_idx);
+
+	kvm->arch.secure_guest = 0;
+	uv_svm_terminate(kvm->arch.lpid);
+
+	return H_PARAMETER;
+}
+
 /*
  * Get a free device PFN from the pool
  *
-- 
2.17.2