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authorMichael Ellerman <mpe@ellerman.id.au>2018-01-09 19:07:15 +0300
committerMichael Ellerman <mpe@ellerman.id.au>2018-01-10 13:27:06 +0300
commitaa8a5e0062ac940f7659394f4817c948dc8c0667 (patch)
treed1c50c8888d06aa876544559cc17319d78d2f798 /arch/powerpc/include/asm/feature-fixups.h
parentc7305645eb0c1621351cfc104038831ae87c0053 (diff)
downloadlinux-aa8a5e0062ac940f7659394f4817c948dc8c0667.tar.xz
powerpc/64s: Add support for RFI flush of L1-D cache
On some CPUs we can prevent the Meltdown vulnerability by flushing the L1-D cache on exit from kernel to user mode, and from hypervisor to guest. This is known to be the case on at least Power7, Power8 and Power9. At this time we do not know the status of the vulnerability on other CPUs such as the 970 (Apple G5), pasemi CPUs (AmigaOne X1000) or Freescale CPUs. As more information comes to light we can enable this, or other mechanisms on those CPUs. The vulnerability occurs when the load of an architecturally inaccessible memory region (eg. userspace load of kernel memory) is speculatively executed to the point where its result can influence the address of a subsequent speculatively executed load. In order for that to happen, the first load must hit in the L1, because before the load is sent to the L2 the permission check is performed. Therefore if no kernel addresses hit in the L1 the vulnerability can not occur. We can ensure that is the case by flushing the L1 whenever we return to userspace. Similarly for hypervisor vs guest. In order to flush the L1-D cache on exit, we add a section of nops at each (h)rfi location that returns to a lower privileged context, and patch that with some sequence. Newer firmwares are able to advertise to us that there is a special nop instruction that flushes the L1-D. If we do not see that advertised, we fall back to doing a displacement flush in software. For guest kernels we support migration between some CPU versions, and different CPUs may use different flush instructions. So that we are prepared to migrate to a machine with a different flush instruction activated, we may have to patch more than one flush instruction at boot if the hypervisor tells us to. In the end this patch is mostly the work of Nicholas Piggin and Michael Ellerman. However a cast of thousands contributed to analysis of the issue, earlier versions of the patch, back ports testing etc. Many thanks to all of them. Tested-by: Jon Masters <jcm@redhat.com> Signed-off-by: Nicholas Piggin <npiggin@gmail.com> Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Diffstat (limited to 'arch/powerpc/include/asm/feature-fixups.h')
-rw-r--r--arch/powerpc/include/asm/feature-fixups.h13
1 files changed, 13 insertions, 0 deletions
diff --git a/arch/powerpc/include/asm/feature-fixups.h b/arch/powerpc/include/asm/feature-fixups.h
index 8f88f771cc55..1e82eb3caabd 100644
--- a/arch/powerpc/include/asm/feature-fixups.h
+++ b/arch/powerpc/include/asm/feature-fixups.h
@@ -187,7 +187,20 @@ label##3: \
FTR_ENTRY_OFFSET label##1b-label##3b; \
.popsection;
+#define RFI_FLUSH_FIXUP_SECTION \
+951: \
+ .pushsection __rfi_flush_fixup,"a"; \
+ .align 2; \
+952: \
+ FTR_ENTRY_OFFSET 951b-952b; \
+ .popsection;
+
+
#ifndef __ASSEMBLY__
+#include <linux/types.h>
+
+extern long __start___rfi_flush_fixup, __stop___rfi_flush_fixup;
+
void apply_feature_fixups(void);
void setup_feature_keys(void);
#endif