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Date:   Fri, 29 Jul 2022 16:05:29 +0200
From:   Borislav Petkov <bp@alien8.de>
To:     Pawan Gupta <pawan.kumar.gupta@linux.intel.com>
Cc:     Jonathan Corbet <corbet@lwn.net>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>,
        Dave Hansen <dave.hansen@linux.intel.com>, x86@kernel.org,
        "H. Peter Anvin" <hpa@zytor.com>, linux-doc@vger.kernel.org,
        linux-kernel@vger.kernel.org, stable@vger.kernel.org,
        tony.luck@intel.com, antonio.gomez.iglesias@linux.intel.com,
        Daniel Sneddon <daniel.sneddon@linux.intel.com>,
        andrew.cooper3@citrix.com, Josh Poimboeuf <jpoimboe@kernel.org>
Subject: Re: [RESEND RFC PATCH] x86/bugs: Add "unknown" reporting for MMIO
 Stale Data
Message-ID: <YuPpKa6OsG9e9nTj@zn.tnic>
References: <a932c154772f2121794a5f2eded1a11013114711.1657846269.git.pawan.kumar.gupta@linux.intel.com>
 <YuJ6TQpSTIeXLNfB@zn.tnic>
 <20220729022851.mdj3wuevkztspodh@desk>
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On Thu, Jul 28, 2022 at 07:28:51PM -0700, Pawan Gupta wrote:
> To keep things simple, can this stay in cpu/common.c?

I know, right?

The gullible maintainer should simply take your half-baked patch so that
you can check off that box and then he can clean it up later.

So you've been doing this kernel development thing for a while. Didn't
it get obvious by now that we don't do half-baked?!

See if this works:

---
diff --git a/Documentation/admin-guide/hw-vuln/processor_mmio_stale_data.rst b/Documentation/admin-guide/hw-vuln/processor_mmio_stale_data.rst
index 9393c50b5afc..14cd3c6ddec6 100644
--- a/Documentation/admin-guide/hw-vuln/processor_mmio_stale_data.rst
+++ b/Documentation/admin-guide/hw-vuln/processor_mmio_stale_data.rst
@@ -230,6 +230,21 @@ The possible values in this file are:
      * - 'Mitigation: Clear CPU buffers'
        - The processor is vulnerable and the CPU buffer clearing mitigation is
          enabled.
+     * - 'Unknown: CPU is beyond its servicing period'
+       - The processor vulnerability status is unknown because it is
+	 out of Servicing period. Mitigation is not attempted.
+
+
+Definitions:
+------------
+
+Servicing period: The process of providing functional and security
+updates to Intel processors or platforms, utilizing the Intel Platform
+Update (IPU) process or other similar mechanisms.
+
+End of Servicing Updates (ESU): ESU is the date at which Intel will no
+longer provide Servicing, such as through IPU or other similar update
+processes. ESU dates will typically be aligned to end of quarter.
 
 If the processor is vulnerable then the following information is appended to
 the above information:
diff --git a/arch/x86/include/asm/cpufeature.h b/arch/x86/include/asm/cpufeature.h
index ea34cc31b047..fe66e94d7b86 100644
--- a/arch/x86/include/asm/cpufeature.h
+++ b/arch/x86/include/asm/cpufeature.h
@@ -154,6 +154,7 @@ extern void clear_cpu_cap(struct cpuinfo_x86 *c, unsigned int bit);
 } while (0)
 
 #define setup_force_cpu_bug(bit) setup_force_cpu_cap(bit)
+#define setup_clear_cpu_bug(bit) setup_clear_cpu_cap(bit)
 
 #if defined(__clang__) && !defined(CONFIG_CC_HAS_ASM_GOTO)
 
diff --git a/arch/x86/include/asm/cpufeatures.h b/arch/x86/include/asm/cpufeatures.h
index 5fe7f6c8a7a4..130cb46ecaf9 100644
--- a/arch/x86/include/asm/cpufeatures.h
+++ b/arch/x86/include/asm/cpufeatures.h
@@ -454,7 +454,8 @@
 #define X86_BUG_TAA			X86_BUG(22) /* CPU is affected by TSX Async Abort(TAA) */
 #define X86_BUG_ITLB_MULTIHIT		X86_BUG(23) /* CPU may incur MCE during certain page attribute changes */
 #define X86_BUG_SRBDS			X86_BUG(24) /* CPU may leak RNG bits if not mitigated */
-#define X86_BUG_MMIO_STALE_DATA		X86_BUG(25) /* CPU is affected by Processor MMIO Stale Data vulnerabilities */
-#define X86_BUG_RETBLEED		X86_BUG(26) /* CPU is affected by RETBleed */
+#define X86_BUG_MMIO_UNKNOWN		X86_BUG(25) /* CPU is too old and its MMIO Stale Data status is unknown */
+#define X86_BUG_MMIO_STALE_DATA		X86_BUG(26) /* CPU is affected by Processor MMIO Stale Data vulnerabilities */
+#define X86_BUG_RETBLEED		X86_BUG(27) /* CPU is affected by RETBleed */
 
 #endif /* _ASM_X86_CPUFEATURES_H */
diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
index 6454bc767f0f..a83d1c4265ae 100644
--- a/arch/x86/kernel/cpu/bugs.c
+++ b/arch/x86/kernel/cpu/bugs.c
@@ -433,7 +433,8 @@ static void __init mmio_select_mitigation(void)
 	u64 ia32_cap;
 
 	if (!boot_cpu_has_bug(X86_BUG_MMIO_STALE_DATA) ||
-	    cpu_mitigations_off()) {
+	     boot_cpu_has_bug(X86_BUG_MMIO_UNKNOWN) ||
+	     cpu_mitigations_off()) {
 		mmio_mitigation = MMIO_MITIGATION_OFF;
 		return;
 	}
@@ -2247,6 +2248,9 @@ static ssize_t tsx_async_abort_show_state(char *buf)
 
 static ssize_t mmio_stale_data_show_state(char *buf)
 {
+	if (boot_cpu_has_bug(X86_BUG_MMIO_UNKNOWN))
+		return sysfs_emit(buf, "Unknown: CPU is beyond its servicing period\n");
+
 	if (mmio_mitigation == MMIO_MITIGATION_OFF)
 		return sysfs_emit(buf, "%s\n", mmio_strings[mmio_mitigation]);
 
@@ -2378,6 +2382,7 @@ static ssize_t cpu_show_common(struct device *dev, struct device_attribute *attr
 		return srbds_show_state(buf);
 
 	case X86_BUG_MMIO_STALE_DATA:
+	case X86_BUG_MMIO_UNKNOWN:
 		return mmio_stale_data_show_state(buf);
 
 	case X86_BUG_RETBLEED:
@@ -2437,7 +2442,10 @@ ssize_t cpu_show_srbds(struct device *dev, struct device_attribute *attr, char *
 
 ssize_t cpu_show_mmio_stale_data(struct device *dev, struct device_attribute *attr, char *buf)
 {
-	return cpu_show_common(dev, attr, buf, X86_BUG_MMIO_STALE_DATA);
+	if (boot_cpu_has_bug(X86_BUG_MMIO_UNKNOWN))
+		return cpu_show_common(dev, attr, buf, X86_BUG_MMIO_UNKNOWN);
+	else
+		return cpu_show_common(dev, attr, buf, X86_BUG_MMIO_STALE_DATA);
 }
 
 ssize_t cpu_show_retbleed(struct device *dev, struct device_attribute *attr, char *buf)
diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
index 736262a76a12..fb3e8576a3b4 100644
--- a/arch/x86/kernel/cpu/common.c
+++ b/arch/x86/kernel/cpu/common.c
@@ -1356,9 +1356,13 @@ static void __init cpu_set_bug_bits(struct cpuinfo_x86 *c)
 	 * but for virtualization case check for ARCH_CAP MSR bits also, VMM may
 	 * not want the guest to enumerate the bug.
 	 */
-	if (cpu_matches(cpu_vuln_blacklist, MMIO) &&
-	    !arch_cap_mmio_immune(ia32_cap))
-		setup_force_cpu_bug(X86_BUG_MMIO_STALE_DATA);
+	if (boot_cpu_has_bug(X86_BUG_MMIO_UNKNOWN)) {
+		if (cpu_matches(cpu_vuln_blacklist, MMIO) &&
+		    !arch_cap_mmio_immune(ia32_cap)) {
+			setup_clear_cpu_bug(X86_BUG_MMIO_UNKNOWN);
+			setup_force_cpu_bug(X86_BUG_MMIO_STALE_DATA);
+		}
+	}
 
 	if (!cpu_has(c, X86_FEATURE_BTC_NO)) {
 		if (cpu_matches(cpu_vuln_blacklist, RETBLEED) || (ia32_cap & ARCH_CAP_RSBA))
diff --git a/arch/x86/kernel/cpu/intel.c b/arch/x86/kernel/cpu/intel.c
index 663f6e6dd288..5b2508adc38a 100644
--- a/arch/x86/kernel/cpu/intel.c
+++ b/arch/x86/kernel/cpu/intel.c
@@ -372,6 +372,10 @@ static void early_init_intel(struct cpuinfo_x86 *c)
 static void bsp_init_intel(struct cpuinfo_x86 *c)
 {
 	resctrl_cpu_detect(c);
+
+	/* Set on older crap */
+	if (c->x86_model < INTEL_FAM6_IVYBRIDGE)
+		setup_force_cpu_bug(X86_BUG_MMIO_UNKNOWN);
 }
 
 #ifdef CONFIG_X86_32


-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette