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Subject[GIT pull] x86 fix for 4.15
Linus,

please pull the latest x86-urgent-for-linus git tree from:

git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git x86-urgent-for-linus

A single fix for the WBINVD issue introduced by the SME support which
causes kexec fails on non AMD/SME capable CPUs. Issue WBINVD only when the
CPU has SME and avoid doing so in a loop.

Thanks,

tglx

------------------>
Tom Lendacky (1):
x86/mm: Rework wbinvd, hlt operation in stop_this_cpu()


arch/x86/kernel/process.c | 25 +++++++++++++++----------
1 file changed, 15 insertions(+), 10 deletions(-)

diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c
index 832a6acd730f..cb368c2a22ab 100644
--- a/arch/x86/kernel/process.c
+++ b/arch/x86/kernel/process.c
@@ -380,19 +380,24 @@ void stop_this_cpu(void *dummy)
disable_local_APIC();
mcheck_cpu_clear(this_cpu_ptr(&cpu_info));

+ /*
+ * Use wbinvd on processors that support SME. This provides support
+ * for performing a successful kexec when going from SME inactive
+ * to SME active (or vice-versa). The cache must be cleared so that
+ * if there are entries with the same physical address, both with and
+ * without the encryption bit, they don't race each other when flushed
+ * and potentially end up with the wrong entry being committed to
+ * memory.
+ */
+ if (boot_cpu_has(X86_FEATURE_SME))
+ native_wbinvd();
for (;;) {
/*
- * Use wbinvd followed by hlt to stop the processor. This
- * provides support for kexec on a processor that supports
- * SME. With kexec, going from SME inactive to SME active
- * requires clearing cache entries so that addresses without
- * the encryption bit set don't corrupt the same physical
- * address that has the encryption bit set when caches are
- * flushed. To achieve this a wbinvd is performed followed by
- * a hlt. Even if the processor is not in the kexec/SME
- * scenario this only adds a wbinvd to a halting processor.
+ * Use native_halt() so that memory contents don't change
+ * (stack usage and variables) after possibly issuing the
+ * native_wbinvd() above.
*/
- asm volatile("wbinvd; hlt" : : : "memory");
+ native_halt();
}
}

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