Prepare pmap for using the AMD SEV C-bit to encrypt guest memory.

The C-bit in a page table entry is used by a SEV guest to specify,
which pages are to be encrypted and which not.  The latter is needed
to share pages with the hypervisor for virtio(4).
The actual position of the C-bit within a PTE is CPU implementation
dependend and needs to be determined dynamically at system boot.
The position of the C-bit also determines the actual size of page
frame mask.  This will be provided by a separate change.
To be able to use the same kernel as both host and guest, the C-bit
is provided as variable similar to the NX-bit.  Same holds for the
page frame masks.
Right now, pg_crypt is set to 0, pg_frame an pg_lgframe to PG_FRAME
and PG_LGFRAME respectively.  Thus the kernel works as a host system
same as before.
Also introduce a PMAP_NOCRYPT flag.  A guest will use this with
busdma to establish unencrypted mappings that can be shared with
the hypervisor.

from hshoexer@; OK mlarkin@

2 files changed, 4 insertions, 2 deletions

diff --git a/sys/arch/amd64/include/pmap.h b/sys/arch/amd64/include/pmap.h
index 326050f4642..6a8e4f92dd3 100644
--- a/sys/arch/amd64/include/pmap.h
+++ b/sys/arch/amd64/include/pmap.h
@@ -1,4 +1,4 @@
-/*	$OpenBSD: pmap.h,v 1.88 2023/12/29 13:23:28 jca Exp $	*/
+/*	$OpenBSD: pmap.h,v 1.89 2024/07/09 19:11:06 bluhm Exp $	*/
 /*	$NetBSD: pmap.h,v 1.1 2003/04/26 18:39:46 fvdl Exp $	*/
 
 /*
@@ -320,6 +320,7 @@ struct pmap {
 };
 
 #define PMAP_EFI	PMAP_MD0
+#define PMAP_NOCRYPT	PMAP_MD1
 
 /*
  * MD flags that we use for pmap_enter (in the pa):
diff --git a/sys/arch/amd64/include/pte.h b/sys/arch/amd64/include/pte.h
index c2bd8793c7d..7d7608efe46 100644
--- a/sys/arch/amd64/include/pte.h
+++ b/sys/arch/amd64/include/pte.h
@@ -1,4 +1,4 @@
-/*	$OpenBSD: pte.h,v 1.17 2023/01/20 16:01:04 deraadt Exp $	*/
+/*	$OpenBSD: pte.h,v 1.18 2024/07/09 19:11:06 bluhm Exp $	*/
 /*	$NetBSD: pte.h,v 1.1 2003/04/26 18:39:47 fvdl Exp $	*/
 
 /*
@@ -164,6 +164,7 @@ typedef u_int64_t pt_entry_t;		/* PTE */
 #ifdef _KERNEL
 extern pt_entry_t pg_xo;	/* XO pte bits using PKU key1 */
 extern pt_entry_t pg_nx;	/* NX pte bit */
+extern pt_entry_t pg_crypt;	/* C pte bit */
 extern pt_entry_t pg_g_kern;	/* PG_G if glbl mappings can be used in kern */
 #endif /* _KERNEL */