KVM: PPC: Book3S 64: Move hcall early register setup to KVM

System calls / hcalls have a different calling convention than
other interrupts, so there is code in the KVMTEST to massage these
into the same form as other interrupt handlers.

Move this work into the KVM hcall handler. This means teaching KVM
a little more about the low level interrupt handler setup, PACA save
areas, etc., although that's not obviously worse than the current
approach of coming up with an entirely different interrupt register
/ save convention.

Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Reviewed-by: Fabiano Rosas <farosas@linux.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20210528090752.3542186-5-npiggin@gmail.com

arch/powerpc/include/asm/exception-64s.h

@@ -35,6 +35,19 @@
 /* PACA save area size in u64 units (exgen, exmc, etc) */
 #define EX_SIZE		10
 
+/* PACA save area offsets */
+#define EX_R9		0
+#define EX_R10		8
+#define EX_R11		16
+#define EX_R12		24
+#define EX_R13		32
+#define EX_DAR		40
+#define EX_DSISR	48
+#define EX_CCR		52
+#define EX_CFAR		56
+#define EX_PPR		64
+#define EX_CTR		72
+
 /*
  * maximum recursive depth of MCE exceptions
  */

arch/powerpc/kernel/exceptions-64s.S

@@ -21,22 +21,6 @@
 #include <asm/feature-fixups.h>
 #include <asm/kup.h>
 
-/* PACA save area offsets (exgen, exmc, etc) */
-#define EX_R9		0
-#define EX_R10		8
-#define EX_R11		16
-#define EX_R12		24
-#define EX_R13		32
-#define EX_DAR		40
-#define EX_DSISR	48
-#define EX_CCR		52
-#define EX_CFAR		56
-#define EX_PPR		64
-#define EX_CTR		72
-.if EX_SIZE != 10
-	.error "EX_SIZE is wrong"
-.endif
-
 /*
  * Following are fixed section helper macros.
  *
@@ -1941,29 +1925,8 @@ EXC_VIRT_END(system_call, 0x4c00, 0x100)
 
 #ifdef CONFIG_KVM_BOOK3S_64_HANDLER
 TRAMP_REAL_BEGIN(system_call_kvm)
-	/*
-	 * This is a hcall, so register convention is as above, with these
-	 * differences:
-	 * r13 = PACA
-	 * ctr = orig r13
-	 * orig r10 saved in PACA
-	 */
-	 /*
-	  * Save the PPR (on systems that support it) before changing to
-	  * HMT_MEDIUM. That allows the KVM code to save that value into the
-	  * guest state (it is the guest's PPR value).
-	  */
-BEGIN_FTR_SECTION
-	mfspr	r10,SPRN_PPR
-	std	r10,HSTATE_PPR(r13)
-END_FTR_SECTION_IFSET(CPU_FTR_HAS_PPR)
-	HMT_MEDIUM
 	mfctr	r10
-	SET_SCRATCH0(r10)
-	mfcr	r10
-	std	r12,HSTATE_SCRATCH0(r13)
-	sldi	r12,r10,32
-	ori	r12,r12,0xc00
+	SET_SCRATCH0(r10) /* Save r13 in SCRATCH0 */
 #ifdef CONFIG_RELOCATABLE
 	/*
 	 * Requires __LOAD_FAR_HANDLER beause kvmppc_hcall lives
@@ -1971,15 +1934,12 @@ END_FTR_SECTION_IFSET(CPU_FTR_HAS_PPR)
 	 */
 	__LOAD_FAR_HANDLER(r10, kvmppc_hcall)
 	mtctr   r10
-	ld	r10,PACA_EXGEN+EX_R10(r13)
 	bctr
 #else
-	ld	r10,PACA_EXGEN+EX_R10(r13)
 	b       kvmppc_hcall
 #endif
 #endif
 
-
 /**
  * Interrupt 0xd00 - Trace Interrupt.
  * This is a synchronous interrupt in response to instruction step or

arch/powerpc/kvm/book3s_64_entry.S

@@ -14,6 +14,36 @@
 .global	kvmppc_hcall
 .balign IFETCH_ALIGN_BYTES
 kvmppc_hcall:
+	/*
+	 * This is a hcall, so register convention is as
+	 * Documentation/powerpc/papr_hcalls.rst, with these additions:
+	 * R13		= PACA
+	 * guest R13 saved in SPRN_SCRATCH0
+	 * R10		= free
+	 * guest r10 saved in PACA_EXGEN
+	 *
+	 * This may also be a syscall from PR-KVM userspace that is to be
+	 * reflected to the PR guest kernel, so registers may be set up for
+	 * a system call rather than hcall. We don't currently clobber
+	 * anything here, but the 0xc00 handler has already clobbered CTR
+	 * and CR0, so PR-KVM can not support a guest kernel that preserves
+	 * those registers across its system calls.
+	 */
+	 /*
+	  * Save the PPR (on systems that support it) before changing to
+	  * HMT_MEDIUM. That allows the KVM code to save that value into the
+	  * guest state (it is the guest's PPR value).
+	  */
+BEGIN_FTR_SECTION
+	mfspr	r10,SPRN_PPR
+	std	r10,HSTATE_PPR(r13)
+END_FTR_SECTION_IFSET(CPU_FTR_HAS_PPR)
+	HMT_MEDIUM
+	mfcr	r10
+	std	r12,HSTATE_SCRATCH0(r13)
+	sldi	r12,r10,32
+	ori	r12,r12,0xc00
+	ld	r10,PACA_EXGEN+EX_R10(r13)
 
 .global	kvmppc_interrupt
 .balign IFETCH_ALIGN_BYTES