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x86: Support kmap_local() forced debugging

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kmap_local() and related interfaces are NOOPs on 64bit and only create
temporary fixmaps for highmem pages on 32bit. That means the test coverage
for this code is pretty small.

CONFIG_KMAP_LOCAL can be enabled independent from CONFIG_HIGHMEM, which
allows to provide support for enforced kmap_local() debugging even on
64bit.

For 32bit the support is unconditional, for 64bit it's only supported when
CONFIG_NR_CPUS <= 4096 as supporting it for 8192 CPUs would require to set
up yet another fixmap PGT.

If CONFIG_KMAP_LOCAL_FORCE_DEBUG is enabled then kmap_local()/kmap_atomic()
will use the temporary fixmap mapping path.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/r/20201118204007.169209557@linutronix.de
This commit is contained in:
Thomas Gleixner
2020-11-18 20:48:41 +01:00
parent 0e91a0c698
commit 14df326702
3 changed files with 15 additions and 4 deletions
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12
arch/x86/include/asm/fixmap.h
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@ -14,13 +14,20 @@
#ifndef _ASM_X86_FIXMAP_H
#define _ASM_X86_FIXMAP_H
#include <asm/kmap_size.h>
/*
* Exposed to assembly code for setting up initial page tables. Cannot be
* calculated in assembly code (fixmap entries are an enum), but is sanity
* checked in the actual fixmap C code to make sure that the fixmap is
* covered fully.
*/
#define FIXMAP_PMD_NUM 2
#ifndef CONFIG_DEBUG_KMAP_LOCAL_FORCE_MAP
# define FIXMAP_PMD_NUM 2
#else
# define KM_PMDS (KM_MAX_IDX * ((CONFIG_NR_CPUS + 511) / 512))
# define FIXMAP_PMD_NUM (KM_PMDS + 2)
#endif
/* fixmap starts downwards from the 507th entry in level2_fixmap_pgt */
#define FIXMAP_PMD_TOP 507
@ -31,7 +38,6 @@
#include <asm/pgtable_types.h>
#ifdef CONFIG_X86_32
#include <linux/threads.h>
#include <asm/kmap_size.h>
#else
#include <uapi/asm/vsyscall.h>
#endif
@ -92,7 +98,7 @@ enum fixed_addresses {
FIX_IO_APIC_BASE_0,
FIX_IO_APIC_BASE_END = FIX_IO_APIC_BASE_0 + MAX_IO_APICS - 1,
#endif
#ifdef CONFIG_X86_32
#ifdef CONFIG_KMAP_LOCAL
FIX_KMAP_BEGIN, /* reserved pte's for temporary kernel mappings */
FIX_KMAP_END = FIX_KMAP_BEGIN + (KM_MAX_IDX * NR_CPUS) - 1,
#ifdef CONFIG_PCI_MMCONFIG