Re: [PATCH v2 03/12] x86/sev: Add an x86 version of prot_guest_has()

From: Tom Lendacky
Date: Sun Aug 15 2021 - 09:53:45 EST


On 8/14/21 2:08 PM, Borislav Petkov wrote:
On Fri, Aug 13, 2021 at 11:59:22AM -0500, Tom Lendacky wrote:
diff --git a/arch/x86/include/asm/protected_guest.h b/arch/x86/include/asm/protected_guest.h
new file mode 100644
index 000000000000..51e4eefd9542
--- /dev/null
+++ b/arch/x86/include/asm/protected_guest.h
@@ -0,0 +1,29 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ * Protected Guest (and Host) Capability checks
+ *
+ * Copyright (C) 2021 Advanced Micro Devices, Inc.
+ *
+ * Author: Tom Lendacky <thomas.lendacky@xxxxxxx>
+ */
+
+#ifndef _X86_PROTECTED_GUEST_H
+#define _X86_PROTECTED_GUEST_H
+
+#include <linux/mem_encrypt.h>
+
+#ifndef __ASSEMBLY__
+
+static inline bool prot_guest_has(unsigned int attr)
+{
+#ifdef CONFIG_AMD_MEM_ENCRYPT
+ if (sme_me_mask)
+ return amd_prot_guest_has(attr);
+#endif
+
+ return false;
+}
+
+#endif /* __ASSEMBLY__ */
+
+#endif /* _X86_PROTECTED_GUEST_H */

I think this can be simplified more, diff ontop below:

- no need for the ifdeffery as amd_prot_guest_has() has versions for
both when CONFIG_AMD_MEM_ENCRYPT is set or not.

Ugh, yeah, not sure why I put that in for this version since I have the static inline for when CONFIG_AMD_MEM_ENCRYPT is not set.


- the sme_me_mask check is pushed there too.

- and since this is vendor-specific, I'm checking the vendor bit. Yeah,
yeah, cross-vendor but I don't really believe that.

It's not a cross-vendor thing as opposed to a KVM or other hypervisor thing where the family doesn't have to be reported as AMD or HYGON. That's why I made the if check be for sme_me_mask. I think that is the safer way to go.

Thanks,
Tom


---
diff --git a/arch/x86/include/asm/protected_guest.h b/arch/x86/include/asm/protected_guest.h
index 51e4eefd9542..8541c76d5da4 100644
--- a/arch/x86/include/asm/protected_guest.h
+++ b/arch/x86/include/asm/protected_guest.h
@@ -12,18 +12,13 @@
#include <linux/mem_encrypt.h>
-#ifndef __ASSEMBLY__
-
static inline bool prot_guest_has(unsigned int attr)
{
-#ifdef CONFIG_AMD_MEM_ENCRYPT
- if (sme_me_mask)
+ if (boot_cpu_data.x86_vendor == X86_VENDOR_AMD ||
+ boot_cpu_data.x86_vendor == X86_VENDOR_HYGON)
return amd_prot_guest_has(attr);
-#endif
return false;
}
-#endif /* __ASSEMBLY__ */
-
#endif /* _X86_PROTECTED_GUEST_H */
diff --git a/arch/x86/mm/mem_encrypt.c b/arch/x86/mm/mem_encrypt.c
index edc67ddf065d..5a0442a6f072 100644
--- a/arch/x86/mm/mem_encrypt.c
+++ b/arch/x86/mm/mem_encrypt.c
@@ -392,6 +392,9 @@ bool noinstr sev_es_active(void)
bool amd_prot_guest_has(unsigned int attr)
{
+ if (!sme_me_mask)
+ return false;
+
switch (attr) {
case PATTR_MEM_ENCRYPT:
return sme_me_mask != 0;