[RFC v2-fix-v5 1/1] x86: Skip WBINVD instruction for VM guest

[Kuppuswamy Sathyanarayanan]

VM guests that supports ACPI, use standard ACPI mechanisms to
signal sleep state entry (including reboot) to the host. The
ACPI specification mandates WBINVD on any sleep state entry
with the expectation that the platform is only responsible for
maintaining the state of memory over sleep states, not
preserving dirty data in any CPU caches. ACPI cache flushing
requirements pre-date the advent of virtualization. Given guest
sleep state entry does not affect any host power rails it is not
required to flush caches. The host is responsible for maintaining
cache state over its own bare metal sleep state transitions that
power-off the cache. A TDX guest, unlike a typical guest, will
machine check if the CPU cache is powered off.
   
Signed-off-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@xxxxxxxxxxxxxxx>
---

Changes since RFC v2-fix-v4:
 * Fixed commit log as per Dan's comments.
 * Used boot_cpu_has(X86_FEATURE_HYPERVISOR) instead of
   prot_guest_has(PR_GUEST_DISABLE_WBINVD) check.
   
Changes since RFC v2-fix-v3:
 * Fixed commit log as per review comments.
 * Instead of fixing all usages of ACPI_FLUSH_CPU_CACHE(),
   created TDX specific exception for it in its implementation.

Changes since RFC v2-fix-v2:
 * Instead of handling WBINVD #VE exception as nop, we skip its
   usage in currently enabled drivers.
 * Adapted commit log for above change.

 arch/x86/include/asm/acenv.h | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/arch/x86/include/asm/acenv.h b/arch/x86/include/asm/acenv.h
index 9aff97f0de7f..d4162e94bee8 100644
--- a/arch/x86/include/asm/acenv.h
+++ b/arch/x86/include/asm/acenv.h
@@ -10,10 +10,15 @@
 #define _ASM_X86_ACENV_H
 
 #include <asm/special_insns.h>
+#include <asm/cpu.h>
 
 /* Asm macros */
 
-#define ACPI_FLUSH_CPU_CACHE()	wbinvd()
+#define ACPI_FLUSH_CPU_CACHE()				\
+do {							\
+	if (!boot_cpu_has(X86_FEATURE_HYPERVISOR))	\
+		wbinvd();				\
+} while (0)
 
 int __acpi_acquire_global_lock(unsigned int *lock);
 int __acpi_release_global_lock(unsigned int *lock);
-- 
2.25.1