[PATCH 4.14 082/159] x86/mm/fixmap: Generalize the GDT fixmap mechanism, introduce struct cpu_entry_area

Greg Kroah-Hartman
2017-12-22T09:40:34Z

From: Andy Lutomirski <luto@kernel.org>

commit ef8813ab280507972bb57e4b1b502811ad4411e9 upstream.

Currently, the GDT is an ad-hoc array of pages, one per CPU, in the
fixmap. Generalize it to be an array of a new 'struct cpu_entry_area'
so that we can cleanly add new things to it.

Signed-off-by: Andy Lutomirski <luto@kernel.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Borislav Petkov <bp@suse.de>
Cc: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Borislav Petkov <bpetkov@suse.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Dave Hansen <dave.hansen@intel.com>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: David Laight <David.Laight@aculab.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: Eduardo Valentin <eduval@amazon.com>
Cc: Greg KH <gregkh@linuxfoundation.org>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Juergen Gross <jgross@suse.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Rik van Riel <riel@redhat.com>
Cc: Will Deacon <will.deacon@arm.com>
Cc: aliguori@amazon.com
Cc: daniel.gruss@iaik.tugraz.at
Cc: hughd@google.com
Cc: keescook@google.com
Link: https://lkml.kernel.org/r/20171204150605.563271721@linutronix.de
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
arch/x86/include/asm/desc.h | 9 +--------
arch/x86/include/asm/fixmap.h | 37 +++++++++++++++++++++++++++++++++++--
arch/x86/kernel/cpu/common.c | 14 +++++++-------
arch/x86/xen/mmu_pv.c | 2 +-
4 files changed, 44 insertions(+), 18 deletions(-)

--- a/arch/x86/include/asm/desc.h
+++ b/arch/x86/include/asm/desc.h
@@ -60,17 +60,10 @@ static inline struct desc_struct *get_cu
return this_cpu_ptr(&gdt_page)->gdt;
}

-/* Get the fixmap index for a specific processor */
-static inline unsigned int get_cpu_gdt_ro_index(int cpu)
-{
- return FIX_GDT_REMAP_END - cpu;
-}
-
/* Provide the fixmap address of the remapped GDT */
static inline struct desc_struct *get_cpu_gdt_ro(int cpu)
{
- unsigned int idx = get_cpu_gdt_ro_index(cpu);
- return (struct desc_struct *)__fix_to_virt(idx);
+ return (struct desc_struct *)&get_cpu_entry_area(cpu)->gdt;
}

/* Provide the current read-only GDT */
--- a/arch/x86/include/asm/fixmap.h
+++ b/arch/x86/include/asm/fixmap.h
@@ -44,6 +44,19 @@ extern unsigned long __FIXADDR_TOP;
PAGE_SIZE)
#endif

+/*
+ * cpu_entry_area is a percpu region in the fixmap that contains things
+ * needed by the CPU and early entry/exit code. Real types aren't used
+ * for all fields here to avoid circular header dependencies.
+ *
+ * Every field is a virtual alias of some other allocated backing store.
+ * There is no direct allocation of a struct cpu_entry_area.
+ */
+struct cpu_entry_area {
+ char gdt[PAGE_SIZE];
+};
+
+#define CPU_ENTRY_AREA_PAGES (sizeof(struct cpu_entry_area) / PAGE_SIZE)

/*
* Here we define all the compile-time 'special' virtual
@@ -101,8 +114,8 @@ enum fixed_addresses {
FIX_LNW_VRTC,
#endif
/* Fixmap entries to remap the GDTs, one per processor. */
- FIX_GDT_REMAP_BEGIN,
- FIX_GDT_REMAP_END = FIX_GDT_REMAP_BEGIN + NR_CPUS - 1,
+ FIX_CPU_ENTRY_AREA_TOP,
+ FIX_CPU_ENTRY_AREA_BOTTOM = FIX_CPU_ENTRY_AREA_TOP + (CPU_ENTRY_AREA_PAGES * NR_CPUS) - 1,

#ifdef CONFIG_ACPI_APEI_GHES
/* Used for GHES mapping from assorted contexts */
@@ -191,5 +204,25 @@ void __init *early_memremap_decrypted_wp
void __early_set_fixmap(enum fixed_addresses idx,
phys_addr_t phys, pgprot_t flags);

+static inline unsigned int __get_cpu_entry_area_page_index(int cpu, int page)
+{
+ BUILD_BUG_ON(sizeof(struct cpu_entry_area) % PAGE_SIZE != 0);
+
+ return FIX_CPU_ENTRY_AREA_BOTTOM - cpu*CPU_ENTRY_AREA_PAGES - page;
+}
+
+#define __get_cpu_entry_area_offset_index(cpu, offset) ({ \
+ BUILD_BUG_ON(offset % PAGE_SIZE != 0); \
+ __get_cpu_entry_area_page_index(cpu, offset / PAGE_SIZE); \
+ })
+
+#define get_cpu_entry_area_index(cpu, field) \
+ __get_cpu_entry_area_offset_index((cpu), offsetof(struct cpu_entry_area, field))
+
+static inline struct cpu_entry_area *get_cpu_entry_area(int cpu)
+{
+ return (struct cpu_entry_area *)__fix_to_virt(__get_cpu_entry_area_page_index(cpu, 0));
+}
+
#endif /* !__ASSEMBLY__ */
#endif /* _ASM_X86_FIXMAP_H */
--- a/arch/x86/kernel/cpu/common.c
+++ b/arch/x86/kernel/cpu/common.c
@@ -466,12 +466,12 @@ void load_percpu_segment(int cpu)
load_stack_canary_segment();
}

-/* Setup the fixmap mapping only once per-processor */
-static inline void setup_fixmap_gdt(int cpu)
+/* Setup the fixmap mappings only once per-processor */
+static inline void setup_cpu_entry_area(int cpu)
{
#ifdef CONFIG_X86_64
/* On 64-bit systems, we use a read-only fixmap GDT. */
- pgprot_t prot = PAGE_KERNEL_RO;
+ pgprot_t gdt_prot = PAGE_KERNEL_RO;
#else
/*
* On native 32-bit systems, the GDT cannot be read-only because
@@ -482,11 +482,11 @@ static inline void setup_fixmap_gdt(int
* On Xen PV, the GDT must be read-only because the hypervisor requires
* it.
*/
- pgprot_t prot = boot_cpu_has(X86_FEATURE_XENPV) ?
+ pgprot_t gdt_prot = boot_cpu_has(X86_FEATURE_XENPV) ?
PAGE_KERNEL_RO : PAGE_KERNEL;
#endif

- __set_fixmap(get_cpu_gdt_ro_index(cpu), get_cpu_gdt_paddr(cpu), prot);
+ __set_fixmap(get_cpu_entry_area_index(cpu, gdt), get_cpu_gdt_paddr(cpu), gdt_prot);
}

/* Load the original GDT from the per-cpu structure */
@@ -1589,7 +1589,7 @@ void cpu_init(void)
if (is_uv_system())
uv_cpu_init();

- setup_fixmap_gdt(cpu);
+ setup_cpu_entry_area(cpu);
load_fixmap_gdt(cpu);
}

@@ -1651,7 +1651,7 @@ void cpu_init(void)

fpu__init_cpu();

- setup_fixmap_gdt(cpu);
+ setup_cpu_entry_area(cpu);
load_fixmap_gdt(cpu);
}
#endif
--- a/arch/x86/xen/mmu_pv.c
+++ b/arch/x86/xen/mmu_pv.c
@@ -2272,7 +2272,7 @@ static void xen_set_fixmap(unsigned idx,
#endif
case FIX_TEXT_POKE0:
case FIX_TEXT_POKE1:
- case FIX_GDT_REMAP_BEGIN ... FIX_GDT_REMAP_END:
+ case FIX_CPU_ENTRY_AREA_TOP ... FIX_CPU_ENTRY_AREA_BOTTOM:
/* All local page mappings */
pte = pfn_pte(phys, prot);
break;