[PATCH] x86/Kconfig: Remove CONFIG_AMD_MEM_ENCRYPT_ACTIVE_BY_DEFAULT

Borislav Petkov
2024-02-02T16:35:40Z

On Thu, Feb 01, 2024 at 05:15:51PM +0100, Ard Biesheuvel wrote:
> OK, I'll remove it in the next rev.

Considering how it simplifies sme_enable() even more, I'd like to
expedite this one.

Thx.

---
From: "Borislav Petkov (AMD)" <bp@alien8.de>
Date: Fri, 2 Feb 2024 17:29:32 +0100
Subject: [PATCH] x86/Kconfig: Remove CONFIG_AMD_MEM_ENCRYPT_ACTIVE_BY_DEFAULT

It was meant well at the time but nothing's using it so get rid of it.

Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
---
Documentation/admin-guide/kernel-parameters.txt | 4 +---
Documentation/arch/x86/amd-memory-encryption.rst | 16 ++++++++--------
arch/x86/Kconfig | 13 -------------
arch/x86/mm/mem_encrypt_identity.c | 11 +----------
4 files changed, 10 insertions(+), 34 deletions(-)

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 31b3a25680d0..2cb70a384af8 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -3320,9 +3320,7 @@

mem_encrypt= [X86-64] AMD Secure Memory Encryption (SME) control
Valid arguments: on, off
- Default (depends on kernel configuration option):
- on (CONFIG_AMD_MEM_ENCRYPT_ACTIVE_BY_DEFAULT=y)
- off (CONFIG_AMD_MEM_ENCRYPT_ACTIVE_BY_DEFAULT=n)
+ Default: off
mem_encrypt=on: Activate SME
mem_encrypt=off: Do not activate SME

diff --git a/Documentation/arch/x86/amd-memory-encryption.rst b/Documentation/arch/x86/amd-memory-encryption.rst
index 07caa8fff852..414bc7402ae7 100644
--- a/Documentation/arch/x86/amd-memory-encryption.rst
+++ b/Documentation/arch/x86/amd-memory-encryption.rst
@@ -87,14 +87,14 @@ The state of SME in the Linux kernel can be documented as follows:
kernel is non-zero).

SME can also be enabled and activated in the BIOS. If SME is enabled and
-activated in the BIOS, then all memory accesses will be encrypted and it will
-not be necessary to activate the Linux memory encryption support. If the BIOS
-merely enables SME (sets bit 23 of the MSR_AMD64_SYSCFG), then Linux can activate
-memory encryption by default (CONFIG_AMD_MEM_ENCRYPT_ACTIVE_BY_DEFAULT=y) or
-by supplying mem_encrypt=on on the kernel command line. However, if BIOS does
-not enable SME, then Linux will not be able to activate memory encryption, even
-if configured to do so by default or the mem_encrypt=on command line parameter
-is specified.
+activated in the BIOS, then all memory accesses will be encrypted and it
+will not be necessary to activate the Linux memory encryption support.
+
+If the BIOS merely enables SME (sets bit 23 of the MSR_AMD64_SYSCFG),
+then memory encryption can be enabled by supplying mem_encrypt=on on the
+kernel command line. However, if BIOS does not enable SME, then Linux
+will not be able to activate memory encryption, even if configured to do
+so by default or the mem_encrypt=on command line parameter is specified.

Secure Nested Paging (SNP)
==========================
diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 5edec175b9bf..58d3593bc4f2 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -1539,19 +1539,6 @@ config AMD_MEM_ENCRYPT
This requires an AMD processor that supports Secure Memory
Encryption (SME).

-config AMD_MEM_ENCRYPT_ACTIVE_BY_DEFAULT
- bool "Activate AMD Secure Memory Encryption (SME) by default"
- depends on AMD_MEM_ENCRYPT
- help
- Say yes to have system memory encrypted by default if running on
- an AMD processor that supports Secure Memory Encryption (SME).
-
- If set to Y, then the encryption of system memory can be
- deactivated with the mem_encrypt=off command line option.
-
- If set to N, then the encryption of system memory can be
- activated with the mem_encrypt=on command line option.
-
# Common NUMA Features
config NUMA
bool "NUMA Memory Allocation and Scheduler Support"
diff --git a/arch/x86/mm/mem_encrypt_identity.c b/arch/x86/mm/mem_encrypt_identity.c
index 7f72472a34d6..efe9f217fcf9 100644
--- a/arch/x86/mm/mem_encrypt_identity.c
+++ b/arch/x86/mm/mem_encrypt_identity.c
@@ -97,7 +97,6 @@ static char sme_workarea[2 * PMD_SIZE] __section(".init.scratch");

static char sme_cmdline_arg[] __initdata = "mem_encrypt";
static char sme_cmdline_on[] __initdata = "on";
-static char sme_cmdline_off[] __initdata = "off";

static void __init sme_clear_pgd(struct sme_populate_pgd_data *ppd)
{
@@ -504,7 +503,7 @@ void __init sme_encrypt_kernel(struct boot_params *bp)

void __init sme_enable(struct boot_params *bp)
{
- const char *cmdline_ptr, *cmdline_arg, *cmdline_on, *cmdline_off;
+ const char *cmdline_ptr, *cmdline_arg, *cmdline_on;
unsigned int eax, ebx, ecx, edx;
unsigned long feature_mask;
unsigned long me_mask;
@@ -587,12 +586,6 @@ void __init sme_enable(struct boot_params *bp)
asm ("lea sme_cmdline_on(%%rip), %0"
: "=r" (cmdline_on)
: "p" (sme_cmdline_on));
- asm ("lea sme_cmdline_off(%%rip), %0"
- : "=r" (cmdline_off)
- : "p" (sme_cmdline_off));
-
- if (IS_ENABLED(CONFIG_AMD_MEM_ENCRYPT_ACTIVE_BY_DEFAULT))
- sme_me_mask = me_mask;

cmdline_ptr = (const char *)((u64)bp->hdr.cmd_line_ptr |
((u64)bp->ext_cmd_line_ptr << 32));
@@ -602,8 +595,6 @@ void __init sme_enable(struct boot_params *bp)

if (!strncmp(buffer, cmdline_on, sizeof(buffer)))
sme_me_mask = me_mask;
- else if (!strncmp(buffer, cmdline_off, sizeof(buffer)))
- sme_me_mask = 0;

out:
if (sme_me_mask) {
--
2.43.0

--
Regards/Gruss,
Boris.