[PATCH 01/13] KVM: PPC: Ultravisor: generic ucall handler plpar_ucall()

[PATCH 01/13] KVM: PPC: Ultravisor: generic ucall handler plpar_ucall()

[Ram Pai]

plpar_ucall() function can now be used to make ucalls
with varied number of in and out arguments. It handles
4 out arguments and a lot of in arguments.

copies the implementation of plpar_hcall().

Signed-off-by: Ram Pai <linuxram@us.ibm.com>
---
 arch/powerpc/platforms/powernv/Makefile |  1 +
 arch/powerpc/platforms/powernv/uvCall.S | 41 +++++++++++++++++++++++++++++++++
 2 files changed, 42 insertions(+)
 create mode 100644 arch/powerpc/platforms/powernv/uvCall.S

diff --git a/arch/powerpc/platforms/powernv/Makefile b/arch/powerpc/platforms/powernv/Makefile
index b540ce8e..5ae1df02 100644
--- a/arch/powerpc/platforms/powernv/Makefile
+++ b/arch/powerpc/platforms/powernv/Makefile
@@ -4,6 +4,7 @@ obj-y			+= opal-rtc.o opal-nvram.o opal-lpc.o opal-flash.o
 obj-y			+= rng.o opal-elog.o opal-dump.o opal-sysparam.o opal-sensor.o
 obj-y			+= opal-msglog.o opal-hmi.o opal-power.o opal-irqchip.o
 obj-y			+= opal-kmsg.o opal-powercap.o opal-psr.o opal-sensor-groups.o
+obj-y			+= uvCall.o
 
 obj-$(CONFIG_SMP)	+= smp.o subcore.o subcore-asm.o
 obj-$(CONFIG_PCI)	+= pci.o pci-ioda.o npu-dma.o pci-ioda-tce.o
diff --git a/arch/powerpc/platforms/powernv/uvCall.S b/arch/powerpc/platforms/powernv/uvCall.S
new file mode 100644
index 0000000..a5e976a
--- /dev/null
+++ b/arch/powerpc/platforms/powernv/uvCall.S
@@ -0,0 +1,41 @@
+/*
+ * This file contains the generic code to perform a ultracall.
+ *
+ * Copyright IBM Corporation 2019.
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation; either version
+ * 2 of the License, or (at your option) any later version.
+ */
+#include <linux/jump_label.h>
+#include <asm/ppc_asm.h>
+#include <asm/asm-offsets.h>
+
+_GLOBAL_TOC(plpar_ucall)
+
+	mfcr	r0
+	stw	r0,8(r1)
+	mr	r0,r3
+
+	std     r4,STK_PARAM(R4)(r1)     /* Save ret buffer */
+
+	mr	r3,r5
+	mr	r4,r6
+	mr	r5,r7
+	mr	r6,r8
+	mr	r7,r9
+	mr	r8,r10
+
+	sc 2				/* invoke the ultravisor */
+
+	ld	r12,STK_PARAM(R4)(r1)
+	std	r4,  0(r12)
+	std	r5,  8(r12)
+	std	r6, 16(r12)
+	std	r7, 24(r12)
+
+	lwz	r0,8(r1)
+	mtcrf	0xff,r0
+
+	blr				/* return r3 = status */
-- 
1.8.3.1

Re: [PATCH 01/13] KVM: PPC: Ultravisor: generic ucall handler plpar_ucall()

[Paul Mackerras]

On Tue, Jan 22, 2019 at 07:59:32AM -0800, Ram Pai wrote:
> plpar_ucall() function can now be used to make ucalls
> with varied number of in and out arguments. It handles
> 4 out arguments and a lot of in arguments.
> 
> copies the implementation of plpar_hcall().
> 
> Signed-off-by: Ram Pai <linuxram@us.ibm.com>
> ---
>  arch/powerpc/platforms/powernv/Makefile |  1 +
>  arch/powerpc/platforms/powernv/uvCall.S | 41 +++++++++++++++++++++++++++++++++

I don't think arch/powerpc/platforms/powernv is the right place for
this, since we will also need to do ucalls from a secure guest and its
kernel may not have CONFIG_PPC_POWERNV=y.  Also, the "plpar_" prefix
gives rise to a cognitive dissonance, because "plpar" is short for
pSeries logical partition, and we definitely are not in a pSeries
logical partition here.

> +_GLOBAL_TOC(plpar_ucall)
> +
> +	mfcr	r0
> +	stw	r0,8(r1)
> +	mr	r0,r3
> +
> +	std     r4,STK_PARAM(R4)(r1)     /* Save ret buffer */
> +
> +	mr	r3,r5
> +	mr	r4,r6
> +	mr	r5,r7
> +	mr	r6,r8
> +	mr	r7,r9
> +	mr	r8,r10
> +
> +	sc 2				/* invoke the ultravisor */
> +
> +	ld	r12,STK_PARAM(R4)(r1)
> +	std	r4,  0(r12)
> +	std	r5,  8(r12)
> +	std	r6, 16(r12)
> +	std	r7, 24(r12)
> +
> +	lwz	r0,8(r1)
> +	mtcrf	0xff,r0
> +
> +	blr				/* return r3 = status */

So we save/restore CR across the ucall, but not LR.  Do we really not
trust the ultravisor to preserve the non-volatile CR fields, or is it
just that you were copying plpar_hcall()?  Either way it deserves a
note in the patch description.

Paul.