[PATCH v2 2/2] x86/dmar: zap DMAR signature for dom0 once in TBOOT case

[PATCH v2 2/2] x86/dmar: zap DMAR signature for dom0 once in TBOOT case

[Zhenzhong Duan]

When TBOOT enabled, acpi_parse_dmar() zap a copy of DMAR table rather
than the real table, so make it controled by config option based on the
fact that we already have done the real zapping in tboot_parse_dmar_table().

As said above, acpi_parse_dmar() doesn't zaps APCI DMAR signature in
real TXT heap table, fix the stale comments.

This is osmetic change, it's unnecessory to zap a copy of DMAR table which
is freed later.

-v2: Add some description per Jan.

Signed-off-by: Zhenzhong Duan <zhenzhong.duan@oracle.com>
---
 xen/arch/x86/tboot.c               |    3 +--
 xen/drivers/passthrough/vtd/dmar.c |    2 ++
 2 files changed, 3 insertions(+), 2 deletions(-)

diff --git a/xen/arch/x86/tboot.c b/xen/arch/x86/tboot.c
index d5a5292..f22fa24 100644
--- a/xen/arch/x86/tboot.c
+++ b/xen/arch/x86/tboot.c
@@ -490,8 +490,7 @@ int __init tboot_parse_dmar_table(acpi_table_handler dmar_handler)
     rc = dmar_handler(dmar_table);
     xfree(dmar_table);
 
-    /* acpi_parse_dmar() zaps APCI DMAR signature in TXT heap table */
-    /* but dom0 will read real table, so must zap it there too */
+    /* Dom0 will read real DMAR table, so must zap it there */
     acpi_dmar_zap();
 
     return rc;
diff --git a/xen/drivers/passthrough/vtd/dmar.c b/xen/drivers/passthrough/vtd/dmar.c
index 8c5fa80..ed4c04e 100644
--- a/xen/drivers/passthrough/vtd/dmar.c
+++ b/xen/drivers/passthrough/vtd/dmar.c
@@ -866,8 +866,10 @@ static int __init acpi_parse_dmar(struct acpi_table_header *table)
     }
 
 out:
+#ifndef CONFIG_TBOOT
     /* Zap ACPI DMAR signature to prevent dom0 using vt-d HW. */
     acpi_dmar_zap();
+#endif
     return ret;
 }
 
-- 
1.7.3

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