X-Git-Url: https://git.kernelconcepts.de/?a=blobdiff_plain;f=arch%2Fx86%2Fentry%2Fentry_64.S;h=055a01de7c8da6e052cfdebe0be8447b14933c87;hb=9e07f98ab76fdeab5629f2f6c977f870a414f1f9;hp=d3033183ed7038ffae691c6784f10a994a0eb765;hpb=31409c97640ff5f1a49e34ac7f3c82097bf57bec;p=karo-tx-linux.git

diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S
index d3033183ed70..055a01de7c8d 100644
--- a/arch/x86/entry/entry_64.S
+++ b/arch/x86/entry/entry_64.S
@@ -1128,7 +1128,18 @@ END(error_exit)
 
 /* Runs on exception stack */
 ENTRY(nmi)
+	/*
+	 * Fix up the exception frame if we're on Xen.
+	 * PARAVIRT_ADJUST_EXCEPTION_FRAME is guaranteed to push at most
+	 * one value to the stack on native, so it may clobber the rdx
+	 * scratch slot, but it won't clobber any of the important
+	 * slots past it.
+	 *
+	 * Xen is a different story, because the Xen frame itself overlaps
+	 * the "NMI executing" variable.
+	 */
 	PARAVIRT_ADJUST_EXCEPTION_FRAME
+
 	/*
 	 * We allow breakpoints in NMIs. If a breakpoint occurs, then
 	 * the iretq it performs will take us out of NMI context.
@@ -1179,9 +1190,12 @@ ENTRY(nmi)
 	 * we don't want to enable interrupts, because then we'll end
 	 * up in an awkward situation in which IRQs are on but NMIs
 	 * are off.
+	 *
+	 * We also must not push anything to the stack before switching
+	 * stacks lest we corrupt the "NMI executing" variable.
 	 */
 
-	SWAPGS
+	SWAPGS_UNSAFE_STACK
 	cld
 	movq	%rsp, %rdx
 	movq	PER_CPU_VAR(cpu_current_top_of_stack), %rsp