powerpc: Ignore DSI error caused by the copy/paste instruction

The data storage interrupt (DSI) error will be generated when the
paste operation is issued on the suspended Nest Accelerator (NX)
window due to NX state changes. The hypervisor expects the
partition to ignore this error during page fault handling.
To differentiate DSI caused by an actual HW configuration or by
the NX window, a new “ibm,pi-features” type value is defined.
Byte 0, bit 3 of pi-attribute-specifier-type is now defined to
indicate this DSI error. If this error is not ignored, the user
space can get SIGBUS when the NX request is issued.

This patch adds changes to read ibm,pi-features property and ignore
DSI error during page fault handling if MMU_FTR_NX_DSI is defined.
Signed-off-by: Haren Myneni <haren@linux.ibm.com>
[mpe: Mention PAPR version in comment]
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/b9cd844b85eb8f70459109ce1b14e44c4cc85fa7.camel@linux.ibm.com

arch/powerpc/include/asm/mmu.h

@@ -120,6 +120,9 @@
  */
 #define MMU_FTR_1T_SEGMENT		ASM_CONST(0x40000000)
 
+// NX paste RMA reject in DSI
+#define MMU_FTR_NX_DSI			ASM_CONST(0x80000000)
+
 /* MMU feature bit sets for various CPUs */
 #define MMU_FTRS_DEFAULT_HPTE_ARCH_V2	(MMU_FTR_HPTE_TABLE | MMU_FTR_TLBIEL | MMU_FTR_16M_PAGE)
 #define MMU_FTRS_POWER		MMU_FTRS_DEFAULT_HPTE_ARCH_V2
@@ -181,7 +184,7 @@ enum {
 #endif
 #ifdef CONFIG_PPC_RADIX_MMU
 		MMU_FTR_TYPE_RADIX |
-		MMU_FTR_GTSE |
+		MMU_FTR_GTSE | MMU_FTR_NX_DSI |
 #endif /* CONFIG_PPC_RADIX_MMU */
 #endif
 #ifdef CONFIG_PPC_KUAP

arch/powerpc/kernel/prom.c

@@ -137,7 +137,7 @@ static void __init move_device_tree(void)
 }
 
 /*
- * ibm,pa-features is a per-cpu property that contains a string of
+ * ibm,pa/pi-features is a per-cpu property that contains a string of
  * attribute descriptors, each of which has a 2 byte header plus up
  * to 254 bytes worth of processor attribute bits.  First header
  * byte specifies the number of bytes following the header.
@@ -149,15 +149,17 @@ static void __init move_device_tree(void)
  * is supported/not supported.  Note that the bit numbers are
  * big-endian to match the definition in PAPR.
  */
-static struct ibm_pa_feature {
+struct ibm_feature {
 	unsigned long	cpu_features;	/* CPU_FTR_xxx bit */
 	unsigned long	mmu_features;	/* MMU_FTR_xxx bit */
 	unsigned int	cpu_user_ftrs;	/* PPC_FEATURE_xxx bit */
 	unsigned int	cpu_user_ftrs2;	/* PPC_FEATURE2_xxx bit */
-	unsigned char	pabyte;		/* byte number in ibm,pa-features */
+	unsigned char	pabyte;		/* byte number in ibm,pa/pi-features */
 	unsigned char	pabit;		/* bit number (big-endian) */
 	unsigned char	invert;		/* if 1, pa bit set => clear feature */
-} ibm_pa_features[] __initdata = {
+};
+
+static struct ibm_feature ibm_pa_features[] __initdata = {
 	{ .pabyte = 0,  .pabit = 0, .cpu_user_ftrs = PPC_FEATURE_HAS_MMU },
 	{ .pabyte = 0,  .pabit = 1, .cpu_user_ftrs = PPC_FEATURE_HAS_FPU },
 	{ .pabyte = 0,  .pabit = 3, .cpu_features  = CPU_FTR_CTRL },
@@ -179,9 +181,19 @@ static struct ibm_pa_feature {
 	{ .pabyte = 64, .pabit = 0, .cpu_features = CPU_FTR_DAWR1 },
 };
 
+/*
+ * ibm,pi-features property provides the support of processor specific
+ * options not described in ibm,pa-features. Right now use byte 0, bit 3
+ * which indicates the occurrence of DSI interrupt when the paste operation
+ * on the suspended NX window.
+ */
+static struct ibm_feature ibm_pi_features[] __initdata = {
+	{ .pabyte = 0, .pabit = 3, .mmu_features  = MMU_FTR_NX_DSI },
+};
+
 static void __init scan_features(unsigned long node, const unsigned char *ftrs,
 				 unsigned long tablelen,
-				 struct ibm_pa_feature *fp,
+				 struct ibm_feature *fp,
 				 unsigned long ft_size)
 {
 	unsigned long i, len, bit;
@@ -218,17 +230,18 @@ static void __init scan_features(unsigned long node, const unsigned char *ftrs,
 	}
 }
 
-static void __init check_cpu_pa_features(unsigned long node)
+static void __init check_cpu_features(unsigned long node, char *name,
+				      struct ibm_feature *fp,
+				      unsigned long size)
 {
 	const unsigned char *pa_ftrs;
 	int tablelen;
 
-	pa_ftrs = of_get_flat_dt_prop(node, "ibm,pa-features", &tablelen);
+	pa_ftrs = of_get_flat_dt_prop(node, name, &tablelen);
 	if (pa_ftrs == NULL)
 		return;
 
-	scan_features(node, pa_ftrs, tablelen,
-		      ibm_pa_features, ARRAY_SIZE(ibm_pa_features));
+	scan_features(node, pa_ftrs, tablelen, fp, size);
 }
 
 #ifdef CONFIG_PPC_64S_HASH_MMU
@@ -380,7 +393,10 @@ static int __init early_init_dt_scan_cpus(unsigned long node,
 			identify_cpu(0, be32_to_cpup(prop));
 
 		check_cpu_feature_properties(node);
-		check_cpu_pa_features(node);
+		check_cpu_features(node, "ibm,pa-features", ibm_pa_features,
+				   ARRAY_SIZE(ibm_pa_features));
+		check_cpu_features(node, "ibm,pi-features", ibm_pi_features,
+				   ARRAY_SIZE(ibm_pi_features));
 	}
 
 	identical_pvr_fixup(node);

arch/powerpc/mm/fault.c

@@ -371,7 +371,22 @@ static void sanity_check_fault(bool is_write, bool is_user,
 #elif defined(CONFIG_PPC_8xx)
 #define page_fault_is_bad(__err)	((__err) & DSISR_NOEXEC_OR_G)
 #elif defined(CONFIG_PPC64)
-#define page_fault_is_bad(__err)	((__err) & DSISR_BAD_FAULT_64S)
+static int page_fault_is_bad(unsigned long err)
+{
+	unsigned long flag = DSISR_BAD_FAULT_64S;
+
+	/*
+	 * PAPR+ v2.11 § 14.15.3.4.1 (unreleased)
+	 * If byte 0, bit 3 of pi-attribute-specifier-type in
+	 * ibm,pi-features property is defined, ignore the DSI error
+	 * which is caused by the paste instruction on the
+	 * suspended NX window.
+	 */
+	if (mmu_has_feature(MMU_FTR_NX_DSI))
+		flag &= ~DSISR_BAD_COPYPASTE;
+
+	return err & flag;
+}
 #else
 #define page_fault_is_bad(__err)	((__err) & DSISR_BAD_FAULT_32S)
 #endif