linux-kernel - [PATCH] x86/cpu/amd: Remove dead code for TSEG region remapping

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Date:   Fri, 27 Nov 2020 12:13:24 -0500
From:   Arvind Sankar <nivedita@...m.mit.edu>
To:     x86@...nel.org, Borislav Petkov <bp@...en8.de>,
        Kim Phillips <kim.phillips@....com>,
        Yazen Ghannam <yazen.ghannam@....com>,
        Tom Lendacky <thomas.lendacky@....com>, Pu Wen <puwen@...on.cn>
Cc:     linux-kernel@...r.kernel.org
Subject: [PATCH] x86/cpu/amd: Remove dead code for TSEG region remapping

Commit
  26bfa5f89486 ("x86, amd: Cleanup init_amd")
moved the code that remaps the TSEG region using 4k pages from
init_amd() to bsp_init_amd().

However, bsp_init_amd() is executed well before the direct mapping is
actually created:

  setup_arch()
    -> early_cpu_init()
      -> early_identify_cpu()
        -> this_cpu->c_bsp_init()
	  -> bsp_init_amd()
    ...
    -> init_mem_mapping()

So the change effectively disabled the 4k remapping, because
pfn_range_is_mapped() is always false at this point.

It has been over six years since the commit, and no-one seems to have
noticed this, so just remove the code. The original code was also
incomplete, since it doesn't check how large the TSEG address range
actually is, so it might remap only part of it in any case.

Hygon has copied the incorrect version, so the code has never run on it
since the cpu support was added two years ago. Remove it from there as
well.

Signed-off-by: Arvind Sankar <nivedita@...m.mit.edu>
---
 arch/x86/kernel/cpu/amd.c   | 21 ---------------------
 arch/x86/kernel/cpu/hygon.c | 20 --------------------
 2 files changed, 41 deletions(-)

diff --git a/arch/x86/kernel/cpu/amd.c b/arch/x86/kernel/cpu/amd.c
index 1f71c7616917..f8ca66f3d861 100644
--- a/arch/x86/kernel/cpu/amd.c
+++ b/arch/x86/kernel/cpu/amd.c
@@ -23,7 +23,6 @@
 
 #ifdef CONFIG_X86_64
 # include <asm/mmconfig.h>
-# include <asm/set_memory.h>
 #endif
 
 #include "cpu.h"
@@ -509,26 +508,6 @@ static void early_init_amd_mc(struct cpuinfo_x86 *c)
 
 static void bsp_init_amd(struct cpuinfo_x86 *c)
 {
-
-#ifdef CONFIG_X86_64
-	if (c->x86 >= 0xf) {
-		unsigned long long tseg;
-
-		/*
-		 * Split up direct mapping around the TSEG SMM area.
-		 * Don't do it for gbpages because there seems very little
-		 * benefit in doing so.
-		 */
-		if (!rdmsrl_safe(MSR_K8_TSEG_ADDR, &tseg)) {
-			unsigned long pfn = tseg >> PAGE_SHIFT;
-
-			pr_debug("tseg: %010llx\n", tseg);
-			if (pfn_range_is_mapped(pfn, pfn + 1))
-				set_memory_4k((unsigned long)__va(tseg), 1);
-		}
-	}
-#endif
-
 	if (cpu_has(c, X86_FEATURE_CONSTANT_TSC)) {
 
 		if (c->x86 > 0x10 ||
diff --git a/arch/x86/kernel/cpu/hygon.c b/arch/x86/kernel/cpu/hygon.c
index dc0840aae26c..ae59115d18f9 100644
--- a/arch/x86/kernel/cpu/hygon.c
+++ b/arch/x86/kernel/cpu/hygon.c
@@ -14,9 +14,6 @@
 #include <asm/cacheinfo.h>
 #include <asm/spec-ctrl.h>
 #include <asm/delay.h>
-#ifdef CONFIG_X86_64
-# include <asm/set_memory.h>
-#endif
 
 #include "cpu.h"
 
@@ -203,23 +200,6 @@ static void early_init_hygon_mc(struct cpuinfo_x86 *c)
 
 static void bsp_init_hygon(struct cpuinfo_x86 *c)
 {
-#ifdef CONFIG_X86_64
-	unsigned long long tseg;
-
-	/*
-	 * Split up direct mapping around the TSEG SMM area.
-	 * Don't do it for gbpages because there seems very little
-	 * benefit in doing so.
-	 */
-	if (!rdmsrl_safe(MSR_K8_TSEG_ADDR, &tseg)) {
-		unsigned long pfn = tseg >> PAGE_SHIFT;
-
-		pr_debug("tseg: %010llx\n", tseg);
-		if (pfn_range_is_mapped(pfn, pfn + 1))
-			set_memory_4k((unsigned long)__va(tseg), 1);
-	}
-#endif
-
 	if (cpu_has(c, X86_FEATURE_CONSTANT_TSC)) {
 		u64 val;
 
-- 
2.26.2