[v5,2/7] powerpc/kernel: Add ucall_norets() ultravisor call handler
diff mbox series

Message ID 20190808040555.2371-3-cclaudio@linux.ibm.com
State New
Headers show
Series
  • kvmppc: Paravirtualize KVM to support ultravisor
Related show

Commit Message

Claudio Carvalho Aug. 8, 2019, 4:05 a.m. UTC
The ultracalls (ucalls for short) allow the Secure Virtual Machines
(SVM)s and hypervisor to request services from the ultravisor such as
accessing a register or memory region that can only be accessed when
running in ultravisor-privileged mode.

This patch adds the ucall_norets() ultravisor call handler. Like
plpar_hcall_norets(), it also saves and restores the Condition
Register (CR).

The specific service needed from an ucall is specified in register
R3 (the first parameter to the ucall). Other parameters to the
ucall, if any, are specified in registers R4 through R12.

Return value of all ucalls is in register R3. Other output values
from the ucall, if any, are returned in registers R4 through R12.

Each ucall returns specific error codes, applicable in the context
of the ucall. However, like with the PowerPC Architecture Platform
Reference (PAPR), if no specific error code is defined for a particular
situation, then the ucall will fallback to an erroneous
parameter-position based code. i.e U_PARAMETER, U_P2, U_P3 etc depending
on the ucall parameter that may have caused the error.

Every host kernel (powernv) needs to be able to do ucalls in case it
ends up being run in a machine with ultravisor enabled. Otherwise, the
kernel may crash early in boot trying to access ultravisor resources,
for instance, trying to set the partition table entry 0. Secure guests
also need to be able to do ucalls and its kernel may not have
CONFIG_PPC_POWERNV=y. For that reason, the ucall.S file is placed under
arch/powerpc/kernel.

If ultravisor is not enabled, the ucalls will be redirected to the
hypervisor which must handle/fail the call.

Thanks to inputs from Ram Pai and Michael Anderson.

Signed-off-by: Claudio Carvalho <cclaudio@linux.ibm.com>

---
Ultravisor call support for secure guests is being proposed as part of
the patchset "Secure Virtual Machine Enablement" posted by Thiago
Bauermann.
---
 arch/powerpc/include/asm/asm-prototypes.h | 11 +++++++++++
 arch/powerpc/include/asm/ultravisor-api.h | 23 +++++++++++++++++++++++
 arch/powerpc/kernel/Makefile              |  1 +
 arch/powerpc/kernel/ucall.S               | 20 ++++++++++++++++++++
 4 files changed, 55 insertions(+)
 create mode 100644 arch/powerpc/include/asm/ultravisor-api.h
 create mode 100644 arch/powerpc/kernel/ucall.S

Comments

Michael Ellerman Aug. 14, 2019, 10:46 a.m. UTC | #1
Claudio Carvalho <cclaudio@linux.ibm.com> writes:
> diff --git a/arch/powerpc/kernel/ucall.S b/arch/powerpc/kernel/ucall.S
> new file mode 100644
> index 000000000000..de9133e45d21
> --- /dev/null
> +++ b/arch/powerpc/kernel/ucall.S
> @@ -0,0 +1,20 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +/*
> + * Generic code to perform an ultravisor call.
> + *
> + * Copyright 2019, IBM Corporation.
> + *
> + */
> +#include <asm/ppc_asm.h>
> +#include <asm/export.h>
> +
> +_GLOBAL(ucall_norets)
> +EXPORT_SYMBOL_GPL(ucall_norets)
> +	mfcr	r0
> +	stw	r0,8(r1)
> +
> +	sc	2		/* Invoke the ultravisor */
> +
> +	lwz	r0,8(r1)
> +	mtcrf	0xff,r0
> +	blr			/* Return r3 = status */

Paulus points that we shouldn't need to save CR here. Our caller will
have already saved it if it needed to, and we don't use CR in this
function so we don't need to save it.

That's assuming the Ultravisor follows the hcall ABI in which CR2-4 are
non-volatile (PAPR § 14.5.3).

I know plpar_hcall_norets() does save CR, but it shouldn't need to, that
seems to be historical. aka. no one knows why it does it but it always
has.

cheers
Segher Boessenkool Aug. 14, 2019, 6:34 p.m. UTC | #2
On Wed, Aug 14, 2019 at 08:46:15PM +1000, Michael Ellerman wrote:
> Claudio Carvalho <cclaudio@linux.ibm.com> writes:
> > +_GLOBAL(ucall_norets)
> > +EXPORT_SYMBOL_GPL(ucall_norets)
> > +	mfcr	r0
> > +	stw	r0,8(r1)
> > +
> > +	sc	2		/* Invoke the ultravisor */
> > +
> > +	lwz	r0,8(r1)
> > +	mtcrf	0xff,r0
> > +	blr			/* Return r3 = status */
> 
> Paulus points that we shouldn't need to save CR here. Our caller will
> have already saved it if it needed to, and we don't use CR in this
> function so we don't need to save it.
> 
> That's assuming the Ultravisor follows the hcall ABI in which CR2-4 are
> non-volatile (PAPR § 14.5.3).

And assuming the ultravisor already clears (or sets, or whatever) all CR
fields it does not want to leak the contents of (which it also should,
of course).

> I know plpar_hcall_norets() does save CR, but it shouldn't need to, that
> seems to be historical. aka. no one knows why it does it but it always
> has.


Segher

Patch
diff mbox series

diff --git a/arch/powerpc/include/asm/asm-prototypes.h b/arch/powerpc/include/asm/asm-prototypes.h
index 296584e6dd55..ee2e67d5a005 100644
--- a/arch/powerpc/include/asm/asm-prototypes.h
+++ b/arch/powerpc/include/asm/asm-prototypes.h
@@ -19,6 +19,7 @@ 
 #include <asm/epapr_hcalls.h>
 #include <asm/dcr.h>
 #include <asm/mmu_context.h>
+#include <asm/ultravisor-api.h>
 
 #include <uapi/asm/ucontext.h>
 
@@ -38,6 +39,16 @@  extern struct static_key hcall_tracepoint_key;
 void __trace_hcall_entry(unsigned long opcode, unsigned long *args);
 void __trace_hcall_exit(long opcode, long retval, unsigned long *retbuf);
 
+/* Ultravisor */
+#ifdef CONFIG_PPC_POWERNV
+long ucall_norets(unsigned long opcode, ...);
+#else
+static inline long ucall_norets(unsigned long opcode, ...)
+{
+	return U_NOT_AVAILABLE;
+}
+#endif
+
 /* OPAL */
 int64_t __opal_call(int64_t a0, int64_t a1, int64_t a2, int64_t a3,
 		    int64_t a4, int64_t a5, int64_t a6, int64_t a7,
diff --git a/arch/powerpc/include/asm/ultravisor-api.h b/arch/powerpc/include/asm/ultravisor-api.h
new file mode 100644
index 000000000000..88ffa78f9d61
--- /dev/null
+++ b/arch/powerpc/include/asm/ultravisor-api.h
@@ -0,0 +1,23 @@ 
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Ultravisor API.
+ *
+ * Copyright 2019, IBM Corporation.
+ *
+ */
+#ifndef _ASM_POWERPC_ULTRAVISOR_API_H
+#define _ASM_POWERPC_ULTRAVISOR_API_H
+
+#include <asm/hvcall.h>
+
+/* Return codes */
+#define U_FUNCTION		H_FUNCTION
+#define U_NOT_AVAILABLE		H_NOT_AVAILABLE
+#define U_P2			H_P2
+#define U_P3			H_P3
+#define U_P4			H_P4
+#define U_P5			H_P5
+#define U_PARAMETER		H_PARAMETER
+#define U_SUCCESS		H_SUCCESS
+
+#endif /* _ASM_POWERPC_ULTRAVISOR_API_H */
diff --git a/arch/powerpc/kernel/Makefile b/arch/powerpc/kernel/Makefile
index 56dfa7a2a6f2..35379b632f3c 100644
--- a/arch/powerpc/kernel/Makefile
+++ b/arch/powerpc/kernel/Makefile
@@ -155,6 +155,7 @@  endif
 
 obj-$(CONFIG_EPAPR_PARAVIRT)	+= epapr_paravirt.o epapr_hcalls.o
 obj-$(CONFIG_KVM_GUEST)		+= kvm.o kvm_emul.o
+obj-$(CONFIG_PPC_POWERNV)	+= ucall.o
 
 # Disable GCOV, KCOV & sanitizers in odd or sensitive code
 GCOV_PROFILE_prom_init.o := n
diff --git a/arch/powerpc/kernel/ucall.S b/arch/powerpc/kernel/ucall.S
new file mode 100644
index 000000000000..de9133e45d21
--- /dev/null
+++ b/arch/powerpc/kernel/ucall.S
@@ -0,0 +1,20 @@ 
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Generic code to perform an ultravisor call.
+ *
+ * Copyright 2019, IBM Corporation.
+ *
+ */
+#include <asm/ppc_asm.h>
+#include <asm/export.h>
+
+_GLOBAL(ucall_norets)
+EXPORT_SYMBOL_GPL(ucall_norets)
+	mfcr	r0
+	stw	r0,8(r1)
+
+	sc	2		/* Invoke the ultravisor */
+
+	lwz	r0,8(r1)
+	mtcrf	0xff,r0
+	blr			/* Return r3 = status */