powerpc/powernv/idle: Restore AMR/UAMOR/AMOR after idle

commit 53a712ba upstream.

In order to implement KUAP (Kernel Userspace Access Protection) on
Power9 we will be using the AMR, and therefore indirectly the
UAMOR/AMOR.

So save/restore these regs in the idle code.
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
[ajd: Backport to 4.19 tree, CVE-2020-11669]
Signed-off-by: Andrew Donnellan <ajd@linux.ibm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

arch/powerpc/kernel/idle_book3s.S

@@ -170,8 +170,11 @@ core_idle_lock_held:
 	bne-	core_idle_lock_held
 	blr
 
-/* Reuse an unused pt_regs slot for IAMR */
+/* Reuse some unused pt_regs slots for AMR/IAMR/UAMOR/UAMOR */
+#define PNV_POWERSAVE_AMR	_TRAP
 #define PNV_POWERSAVE_IAMR	_DAR
+#define PNV_POWERSAVE_UAMOR	_DSISR
+#define PNV_POWERSAVE_AMOR	RESULT
 
 /*
  * Pass requested state in r3:
@@ -205,8 +208,16 @@ pnv_powersave_common:
 	SAVE_NVGPRS(r1)
 
 BEGIN_FTR_SECTION
+	mfspr	r4, SPRN_AMR
 	mfspr	r5, SPRN_IAMR
+	mfspr	r6, SPRN_UAMOR
+	std	r4, PNV_POWERSAVE_AMR(r1)
 	std	r5, PNV_POWERSAVE_IAMR(r1)
+	std	r6, PNV_POWERSAVE_UAMOR(r1)
+BEGIN_FTR_SECTION_NESTED(42)
+	mfspr	r7, SPRN_AMOR
+	std	r7, PNV_POWERSAVE_AMOR(r1)
+END_FTR_SECTION_NESTED_IFSET(CPU_FTR_HVMODE, 42)
 END_FTR_SECTION_IFSET(CPU_FTR_ARCH_207S)
 
 	mfcr	r5
@@ -935,12 +946,20 @@ END_FTR_SECTION_IFSET(CPU_FTR_HVMODE)
 	REST_GPR(2, r1)
 
 BEGIN_FTR_SECTION
-	/* IAMR was saved in pnv_powersave_common() */
+	/* These regs were saved in pnv_powersave_common() */
+	ld	r4, PNV_POWERSAVE_AMR(r1)
 	ld	r5, PNV_POWERSAVE_IAMR(r1)
+	ld	r6, PNV_POWERSAVE_UAMOR(r1)
+	mtspr	SPRN_AMR, r4
 	mtspr	SPRN_IAMR, r5
+	mtspr	SPRN_UAMOR, r6
+BEGIN_FTR_SECTION_NESTED(42)
+	ld	r7, PNV_POWERSAVE_AMOR(r1)
+	mtspr	SPRN_AMOR, r7
+END_FTR_SECTION_NESTED_IFSET(CPU_FTR_HVMODE, 42)
 	/*
-	 * We don't need an isync here because the upcoming mtmsrd is
-	 * execution synchronizing.
+	 * We don't need an isync here after restoring IAMR because the upcoming
+	 * mtmsrd is execution synchronizing.
 	 */
 END_FTR_SECTION_IFSET(CPU_FTR_ARCH_207S)