powerpc/64s: Disallow PROT_SAO in LPARs by default

Since migration of guests using SAO to ISA 3.1 hosts may cause issues,
disable PROT_SAO in LPARs by default and introduce a new Kconfig option
PPC_PROT_SAO_LPAR to allow users to enable it if desired.

Signed-off-by: Shawn Anastasio <shawn@anastas.io>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20200821185558.35561-3-shawn@anastas.io

diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
index 1f48bbf..65bed1f 100644 (file)
--- a/arch/powerpc/Kconfig
+++ b/arch/powerpc/Kconfig
@@ -860,6 +860,18 @@ config PPC_SUBPAGE_PROT
 
          If unsure, say N here.
 
+config PPC_PROT_SAO_LPAR
+       bool "Support PROT_SAO mappings in LPARs"
+       depends on PPC_BOOK3S_64
+       help
+         This option adds support for PROT_SAO mappings from userspace
+         inside LPARs on supported CPUs.
+
+         This may cause issues when performing guest migration from
+         a CPU that supports SAO to one that does not.
+
+         If unsure, say N here.
+
 config PPC_COPRO_BASE
        bool
 

diff --git a/arch/powerpc/include/asm/mman.h b/arch/powerpc/include/asm/mman.h
index 4ba303e..7cb6d18 100644 (file)
--- a/arch/powerpc/include/asm/mman.h
+++ b/arch/powerpc/include/asm/mman.h
@@ -40,8 +40,13 @@ static inline bool arch_validate_prot(unsigned long prot, unsigned long addr)
 {
        if (prot & ~(PROT_READ | PROT_WRITE | PROT_EXEC | PROT_SEM | PROT_SAO))
                return false;
-       if ((prot & PROT_SAO) && !cpu_has_feature(CPU_FTR_SAO))
-               return false;
+       if (prot & PROT_SAO) {
+               if (!cpu_has_feature(CPU_FTR_SAO))
+                       return false;
+               if (firmware_has_feature(FW_FEATURE_LPAR) &&
+                   !IS_ENABLED(CONFIG_PPC_PROT_SAO_LPAR))
+                       return false;
+       }
        return true;
 }
 #define arch_validate_prot arch_validate_prot