Subject: [PATCH] powerpc/book3s64/radix: Add kernel command line option to disable radix GTSE

From: "Aneesh Kumar K.V" <[email-masked]>
Date: Fri, 24 Jul 2020 13:26:00 +0530

This adds a kernel command line option that can be used to disable GTSE support.
Disabling GTSE implies kernel will make hcalls to invalidate TLB entries.

This was done so that we can do VM migration between configs that enable/disable
GTSE support via hypervisor. To migrate a VM from a system that supports
GTSE to a system that doesn't, we can boot the guest with radix_gtse=off, thereby
forcing the guest to use hcalls for TLB invalidates.

The check for hcall availability is done in pSeries_setup_arch so that
the panic message appears on the console. This should only happen on
a hypervisor that doesn't force the guest to hash translation even
though it can't handle the radix GTSE=0 request via CAS. With radix_gtse=off
if the hypervisor doesn't support hcall_rpt_invalidate hcall it should
force the LPAR to hash translation.

Signed-off-by: Aneesh Kumar K.V <[email-masked]>
---
 Documentation/admin-guide/kernel-parameters.txt |  3 +++
 arch/powerpc/include/asm/firmware.h             |  4 +++-
 arch/powerpc/kernel/prom_init.c                 | 13 +++++++++----
 arch/powerpc/platforms/pseries/firmware.c       |  1 +
 arch/powerpc/platforms/pseries/setup.c          |  5 +++++
 5 files changed, 21 insertions(+), 5 deletions(-)

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index fb95fad81c79..df20c98a8920 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -896,6 +896,9 @@
 	disable_radix	[PPC]
 			Disable RADIX MMU mode on POWER9
 
+	radix_gtse=off	[PPC/PSERIES]
+			Disable RADIX GTSE feature.
+
 	disable_tlbie	[PPC]
 			Disable TLBIE instruction. Currently does not work
 			with KVM, with HASH MMU, or with coherent accelerators.
diff --git a/arch/powerpc/include/asm/firmware.h b/arch/powerpc/include/asm/firmware.h
index 6003c2e533a0..aa6a5ef5d483 100644
--- a/arch/powerpc/include/asm/firmware.h
+++ b/arch/powerpc/include/asm/firmware.h
@@ -52,6 +52,7 @@
 #define FW_FEATURE_PAPR_SCM 	ASM_CONST(0x0000002000000000)
 #define FW_FEATURE_ULTRAVISOR	ASM_CONST(0x0000004000000000)
 #define FW_FEATURE_STUFF_TCE	ASM_CONST(0x0000008000000000)
+#define FW_FEATURE_RPT_INVALIDATE ASM_CONST(0x0000010000000000)
 
 #ifndef __ASSEMBLY__
 
@@ -71,7 +72,8 @@ enum {
 		FW_FEATURE_TYPE1_AFFINITY | FW_FEATURE_PRRN |
 		FW_FEATURE_HPT_RESIZE | FW_FEATURE_DRMEM_V2 |
 		FW_FEATURE_DRC_INFO | FW_FEATURE_BLOCK_REMOVE |
-		FW_FEATURE_PAPR_SCM | FW_FEATURE_ULTRAVISOR,
+		FW_FEATURE_PAPR_SCM | FW_FEATURE_ULTRAVISOR |
+		FW_FEATURE_RPT_INVALIDATE,
 	FW_FEATURE_PSERIES_ALWAYS = 0,
 	FW_FEATURE_POWERNV_POSSIBLE = FW_FEATURE_OPAL | FW_FEATURE_ULTRAVISOR,
 	FW_FEATURE_POWERNV_ALWAYS = 0,
diff --git a/arch/powerpc/kernel/prom_init.c b/arch/powerpc/kernel/prom_init.c
index cbc605cfdec0..e7e91965fe6c 100644
--- a/arch/powerpc/kernel/prom_init.c
+++ b/arch/powerpc/kernel/prom_init.c
@@ -169,6 +169,7 @@ static unsigned long __prombss prom_tce_alloc_end;
 
 #ifdef CONFIG_PPC_PSERIES
 static bool __prombss prom_radix_disable;
+static bool __prombss prom_radix_gtse_disable;
 static bool __prombss prom_xive_disable;
 #endif
 
@@ -823,6 +824,12 @@ static void __init early_cmdline_parse(void)
 	if (prom_radix_disable)
 		prom_debug("Radix disabled from cmdline\n");
 
+	opt = prom_strstr(prom_cmd_line, "radix_gtse=off");
+	if (opt) {
+		prom_radix_gtse_disable = true;
+		prom_debug("Radix GTSE disabled from cmdline\n");
+	}
+
 	opt = prom_strstr(prom_cmd_line, "xive=off");
 	if (opt) {
 		prom_xive_disable = true;
@@ -1285,10 +1292,8 @@ static void __init prom_parse_platform_support(u8 index, u8 val,
 		prom_parse_mmu_model(val & OV5_FEAT(OV5_MMU_SUPPORT), support);
 		break;
 	case OV5_INDX(OV5_RADIX_GTSE): /* Radix Extensions */
-		if (val & OV5_FEAT(OV5_RADIX_GTSE)) {
-			prom_debug("Radix - GTSE supported\n");
-			support->radix_gtse = true;
-		}
+		if (val & OV5_FEAT(OV5_RADIX_GTSE))
+			support->radix_gtse = !prom_radix_gtse_disable;
 		break;
 	case OV5_INDX(OV5_XIVE_SUPPORT): /* Interrupt mode */
 		prom_parse_xive_model(val & OV5_FEAT(OV5_XIVE_SUPPORT),
diff --git a/arch/powerpc/platforms/pseries/firmware.c b/arch/powerpc/platforms/pseries/firmware.c
index 3e49cc23a97a..4c7b7f5a2ebc 100644
--- a/arch/powerpc/platforms/pseries/firmware.c
+++ b/arch/powerpc/platforms/pseries/firmware.c
@@ -65,6 +65,7 @@ hypertas_fw_features_table[] = {
 	{FW_FEATURE_HPT_RESIZE,		"hcall-hpt-resize"},
 	{FW_FEATURE_BLOCK_REMOVE,	"hcall-block-remove"},
 	{FW_FEATURE_PAPR_SCM,		"hcall-scm"},
+	{FW_FEATURE_RPT_INVALIDATE,	"hcall-rpt-invalidate"},
 };
 
 /* Build up the firmware features bitmask using the contents of
diff --git a/arch/powerpc/platforms/pseries/setup.c b/arch/powerpc/platforms/pseries/setup.c
index 2db8469e475f..9e5e098665f7 100644
--- a/arch/powerpc/platforms/pseries/setup.c
+++ b/arch/powerpc/platforms/pseries/setup.c
@@ -745,6 +745,11 @@ static void __init pSeries_setup_arch(void)
 	smp_init_pseries();

+	if (radix_enabled() && !mmu_has_feature(MMU_FTR_GTSE))
+		if (!firmware_has_feature(FW_FEATURE_RPT_INVALIDATE))
+			panic("BUG: Radix support requires either GTSE or RPT_INVALIDATE\n");
+
+
 	/* openpic global configuration register (64-bit format). */
 	/* openpic Interrupt Source Unit pointer (64-bit format). */
 	/* python0 facility area (mmio) (64-bit format) REAL address. */
-- 
2.26.2