Commit 14df3267 authored by Thomas Gleixner's avatar Thomas Gleixner
Browse files

x86: Support kmap_local() forced debugging 



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: default avatarThomas Gleixner <tglx@linutronix.de>
Acked-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/r/20201118204007.169209557@linutronix.de
parent 0e91a0c6

arch/x86/Kconfig

+1 −0
Original line number Diff line number Diff line
@@ -93,6 +93,7 @@ config X86 
	select ARCH_SUPPORTS_ACPI

	select ARCH_SUPPORTS_ATOMIC_RMW

	select ARCH_SUPPORTS_NUMA_BALANCING	if X86_64

	select ARCH_SUPPORTS_KMAP_LOCAL_FORCE_MAP	if NR_CPUS <= 4096

	select ARCH_USE_BUILTIN_BSWAP

	select ARCH_USE_QUEUED_RWLOCKS

	select ARCH_USE_QUEUED_SPINLOCKS

arch/x86/include/asm/fixmap.h

+9 −3
Original line number Diff line number Diff line
@@ -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.

 */

#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

arch/x86/include/asm/pgtable_64_types.h

+5 −1
Original line number Diff line number Diff line
@@ -143,7 +143,11 @@ extern unsigned int ptrs_per_p4d; 


#define MODULES_VADDR		(__START_KERNEL_map + KERNEL_IMAGE_SIZE)

/* The module sections ends with the start of the fixmap */

#ifndef CONFIG_DEBUG_KMAP_LOCAL_FORCE_MAP

# define MODULES_END		_AC(0xffffffffff000000, UL)

#else

# define MODULES_END		_AC(0xfffffffffe000000, UL)

#endif

#define MODULES_LEN		(MODULES_END - MODULES_VADDR)



#define ESPFIX_PGD_ENTRY	_AC(-2, UL)