Patch "powerpc/64: Disable use of radix under a hypervisor" has been added to the 4.9-stable tree

This is a note to let you know that I've just added the patch titled

powerpc/64: Disable use of radix under a hypervisor

to the 4.9-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
powerpc-64-disable-use-of-radix-under-a-hypervisor.patch
and it can be found in the queue-4.9 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Paul Mackerras <[email protected]>
Date: Thu, 16 Feb 2017 13:49:21 +1100
Subject: powerpc/64: Disable use of radix under a hypervisor

From: Paul Mackerras <[email protected]>

commit 3f91a89d424a79f8082525db5a375e438887bb3e upstream.

Currently, if the kernel is running on a POWER9 processor under a hypervisor, it may try to use the radix MMU even though it doesn't have the necessary code to do so (it doesn't negotiate use of radix, and it doesn't do the H_REGISTER_PROC_TBL hcall). If the hypervisor supports both radix and HPT, then it will set up the guest to use HPT (since the guest doesn't request radix in the CAS call), but if the radix feature bit is set in the ibm,pa-features property (which is valid, since ibm,pa-features is defined to represent the capabilities of the processor) the guest will try to use radix, resulting in a crash when it turns the MMU on.

This makes the minimal fix for the current code, which is to disable radix unless we are running in hypervisor mode.

---
 arch/powerpc/mm/init_64.c |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

@@ -424,7 +424,8 @@ early_param("disable_radix", parse_disab
 void __init mmu_early_init_devtree(void)
 {
 	/* Disable radix mode based on kernel command line. */
-	if (disable_radix)
+	/* We don't yet have the machinery to do radix as a guest. */
+	if (disable_radix || !(mfmsr() & MSR_HV))
 		cur_cpu_spec->mmu_features &= ~MMU_FTR_TYPE_RADIX;
 
 	if (early_radix_enabled())

Patches currently in stable-queue which might be from [email protected] are

queue-4.9/powerpc-64-disable-use-of-radix-under-a-hypervisor.patch