[PATCH v2] powerpc/pseries: Avoid using addr_to_pfn in realmode

[Ganesh Goudar <ganeshgr@linux.ibm.com>]

When an UE or memory error exception is encountered the MCE handler
tries to find the pfn using addr_to_pfn() which takes effective
address as an argument, later pfn is used to poison the page where
memory error occurred, recent rework in this area made addr_to_pfn
to run in realmode, which can be fatal as it may try to access
memory outside RMO region.

To fix this use addr_to_pfn after switching to virtual mode.

Signed-off-by: Ganesh Goudar <ganeshgr@linux.ibm.com>
---
V2: Leave bare metal code and save_mce_event as is.
---
 arch/powerpc/platforms/pseries/ras.c | 20 +++++++++++---------
 1 file changed, 11 insertions(+), 9 deletions(-)

diff --git a/arch/powerpc/platforms/pseries/ras.c b/arch/powerpc/platforms/pseries/ras.c
index f3736fcd98fc..def875815e92 100644
--- a/arch/powerpc/platforms/pseries/ras.c
+++ b/arch/powerpc/platforms/pseries/ras.c
@@ -610,16 +610,8 @@ static int mce_handle_error(struct pt_regs *regs, struct rtas_error_log *errp)
 		if (mce_log->sub_err_type & UE_EFFECTIVE_ADDR_PROVIDED)
 			eaddr = be64_to_cpu(mce_log->effective_address);
 
-		if (mce_log->sub_err_type & UE_LOGICAL_ADDR_PROVIDED) {
+		if (mce_log->sub_err_type & UE_LOGICAL_ADDR_PROVIDED)
 			paddr = be64_to_cpu(mce_log->logical_address);
-		} else if (mce_log->sub_err_type & UE_EFFECTIVE_ADDR_PROVIDED) {
-			unsigned long pfn;
-
-			pfn = addr_to_pfn(regs, eaddr);
-			if (pfn != ULONG_MAX)
-				paddr = pfn << PAGE_SHIFT;
-		}
-
 		break;
 	case MC_ERROR_TYPE_SLB:
 		mce_err.error_type = MCE_ERROR_TYPE_SLB;
@@ -725,6 +717,16 @@ static int mce_handle_error(struct pt_regs *regs, struct rtas_error_log *errp)
 	 *       SLB multihit is done by now.
 	 */
 	mtmsr(mfmsr() | MSR_IR | MSR_DR);
+
+	/* Use addr_to_pfn after switching to virtual mode */
+	if (!paddr && error_type == MC_ERROR_TYPE_UE &&
+	    mce_log->sub_err_type & UE_EFFECTIVE_ADDR_PROVIDED) {
+		unsigned long pfn;
+
+		pfn = addr_to_pfn(regs, eaddr);
+		if (pfn != ULONG_MAX)
+			paddr = pfn << PAGE_SHIFT;
+	}
 	save_mce_event(regs, disposition == RTAS_DISP_FULLY_RECOVERED,
 			&mce_err, regs->nip, eaddr, paddr);
 
-- 
2.17.2