Re: [RFC][PATCH 11/34] x86/cpu/intel: Prepare MKTME for "address configuration" infrastructure

Kirill A. Shutemov
2024-02-26T12:14:58Z

On Fri, Feb 23, 2024 at 08:22:16AM -0800, Dave Hansen wrote:
> On 2/23/24 03:33, Kirill A. Shutemov wrote:
> > On Thu, Feb 22, 2024 at 10:39:41AM -0800, Dave Hansen wrote:
> >> From: Dave Hansen <dave.hansen@linux.intel.com>
> >>
> >> Intel also does memory encryption and also fiddles with the physical
> >> address bits. This is currently called for *each* CPU, but practically
> >> only done on the boot CPU because of 'mktme_status'.
> >>
> >> Move it from the "each CPU" ->c_init() function to ->c_bsp_init() where
> >> the whole thing only gets called once ever. This also necessitates moving
> >> detect_tme() and its entourage around in the file.
> > The state machine around mktme_state doesn't make sense if we only call it
> > on boot CPU, so detect_tme() can be drastically simplified. I can do it on
> > top of the patchset.
>
> That would be great. Looking at it again, the (tme_activate !=
> tme_activate_cpu0) block is total cruft now. It probably just needs to
> get moved to secondary CPU startup.

I have never saw the check to be useful. I think it can be just dropped.

The patch below makes detect_tme() only enumerate TME and MKTME. And
report number of keyid bits. Kernel doesn't care about anything else.

Any comments?

From 1080535093d21f025d46fd610de5ad788591f4b5 Mon Sep 17 00:00:00 2001
From: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Date: Mon, 26 Feb 2024 14:01:01 +0200
Subject: [PATCH] x86/cpu/intel: Simplify detect_tme()

The detect_tme() function is now only called by the boot CPU. The logic
for cross-checking TME configuration between CPUs is no longer used. It
has never identified a real problem and can be safely removed.

The kernel does not use MKTME and is not concerned with MKTME policy or
encryption algorithms. There is no need to check them.

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
---
arch/x86/kernel/cpu/intel.c | 44 ++-----------------------------------
1 file changed, 2 insertions(+), 42 deletions(-)

diff --git a/arch/x86/kernel/cpu/intel.c b/arch/x86/kernel/cpu/intel.c
index 4192aa4576f4..60918b49344c 100644
--- a/arch/x86/kernel/cpu/intel.c
+++ b/arch/x86/kernel/cpu/intel.c
@@ -329,55 +329,20 @@ static void early_init_intel(struct cpuinfo_x86 *c)
#define TME_ACTIVATE_CRYPTO_ALGS(x) ((x >> 48) & 0xffff) /* Bits 63:48 */
#define TME_ACTIVATE_CRYPTO_AES_XTS_128 1

-/* Values for mktme_status (SW only construct) */
-#define MKTME_ENABLED 0
-#define MKTME_DISABLED 1
-#define MKTME_UNINITIALIZED 2
-static int mktme_status = MKTME_UNINITIALIZED;
-
static int detect_tme(struct cpuinfo_x86 *c)
{
- u64 tme_activate, tme_policy, tme_crypto_algs;
- int keyid_bits = 0, nr_keyids = 0;
- static u64 tme_activate_cpu0 = 0;
+ int keyid_bits, nr_keyids;
+ u64 tme_activate;

rdmsrl(MSR_IA32_TME_ACTIVATE, tme_activate);

- if (mktme_status != MKTME_UNINITIALIZED) {
- if (tme_activate != tme_activate_cpu0) {
- /* Broken BIOS? */
- pr_err_once("x86/tme: configuration is inconsistent between CPUs\n");
- pr_err_once("x86/tme: MKTME is not usable\n");
- mktme_status = MKTME_DISABLED;
-
- /* Proceed. We may need to exclude bits from x86_phys_bits. */
- }
- } else {
- tme_activate_cpu0 = tme_activate;
- }
-
if (!TME_ACTIVATE_LOCKED(tme_activate) || !TME_ACTIVATE_ENABLED(tme_activate)) {
pr_info_once("x86/tme: not enabled by BIOS\n");
- mktme_status = MKTME_DISABLED;
return 0;
}

- if (mktme_status != MKTME_UNINITIALIZED)
- goto detect_keyid_bits;
-
pr_info("x86/tme: enabled by BIOS\n");

- tme_policy = TME_ACTIVATE_POLICY(tme_activate);
- if (tme_policy != TME_ACTIVATE_POLICY_AES_XTS_128)
- pr_warn("x86/tme: Unknown policy is active: %#llx\n", tme_policy);
-
- tme_crypto_algs = TME_ACTIVATE_CRYPTO_ALGS(tme_activate);
- if (!(tme_crypto_algs & TME_ACTIVATE_CRYPTO_AES_XTS_128)) {
- pr_err("x86/mktme: No known encryption algorithm is supported: %#llx\n",
- tme_crypto_algs);
- mktme_status = MKTME_DISABLED;
- }
-detect_keyid_bits:
keyid_bits = TME_ACTIVATE_KEYID_BITS(tme_activate);
nr_keyids = (1UL << keyid_bits) - 1;
if (nr_keyids) {
@@ -387,11 +352,6 @@ static int detect_tme(struct cpuinfo_x86 *c)
pr_info_once("x86/mktme: disabled by BIOS\n");
}

- if (mktme_status == MKTME_UNINITIALIZED) {
- /* MKTME is usable */
- mktme_status = MKTME_ENABLED;
- }
-
return keyid_bits;
}

--
Kiryl Shutsemau / Kirill A. Shutemov