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x86/cpu/amd: Remove dead code for TSEG region remapping 

Commit

  26bfa5f894 ("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.

Committer notes:

This workaround is incomplete anyway:

1. The code must check MSRC001_0113.TValid (SMM TSeg Mask MSR) first, to
check whether the TSeg address range is enabled.

2. The code must check whether the range is not 2M aligned - if it is,
there's nothing to work around.

3. In all the BIOSes tested, the TSeg range is in a e820 reserved area
and those are not mapped anymore, after

  66520ebc2d ("x86, mm: Only direct map addresses that are marked as E820_RAM")

which means, there's nothing to be worked around either.

So let's rip it out.

Signed-off-by: Arvind Sankar <nivedita@alum.mit.edu>
Signed-off-by: Borislav Petkov <bp@suse.de>
Link: https://lkml.kernel.org/r/20201127171324.1846019-1-nivedita@alum.mit.edu
This commit is contained in:
Arvind Sankar 2020-11-27 12:13:24 -05:00 committed by Borislav Petkov
parent cb09a37972
commit 262bd5724a
2 changed files with 0 additions and 41 deletions
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21
arch/x86/kernel/cpu/amd.c
View File

@ -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 ||

20
arch/x86/kernel/cpu/hygon.c
View File

@ -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;