efi: Disable interrupts around EFI calls, not in the epilog/prolog calls

Tapasweni Pathak reported that we do a kmalloc() in efi_call_phys_prolog()
on x86-64 while having interrupts disabled, which is a big no-no, as
kmalloc() can sleep.

Solve this by removing the irq disabling from the prolog/epilog calls
around EFI calls: it's unnecessary, as in this stage we are single
threaded in the boot thread, and we don't ever execute this from
interrupt contexts.
Reported-by: NTapasweni Pathak <tapaswenipathak@gmail.com>
Signed-off-by: NIngo Molnar <mingo@kernel.org>
Signed-off-by: NMatt Fleming <matt.fleming@intel.com>

arch/x86/platform/efi/efi.c

@@ -85,12 +85,19 @@ static efi_status_t __init phys_efi_set_virtual_address_map(
 	efi_memory_desc_t *virtual_map)
 {
 	efi_status_t status;
+	unsigned long flags;
 
 	efi_call_phys_prolog();
+
+	/* Disable interrupts around EFI calls: */
+	local_irq_save(flags);
 	status = efi_call_phys(efi_phys.set_virtual_address_map,
 			       memory_map_size, descriptor_size,
 			       descriptor_version, virtual_map);
+	local_irq_restore(flags);
+
 	efi_call_phys_epilog();
+
 	return status;
 }
 

arch/x86/platform/efi/efi_32.c

@@ -33,11 +33,10 @@
 
 /*
  * To make EFI call EFI runtime service in physical addressing mode we need
- * prolog/epilog before/after the invocation to disable interrupt, to
- * claim EFI runtime service handler exclusively and to duplicate a memory in
- * low memory space say 0 - 3G.
+ * prolog/epilog before/after the invocation to claim the EFI runtime service
+ * handler exclusively and to duplicate a memory mapping in low memory space,
+ * say 0 - 3G.
  */
-static unsigned long efi_rt_eflags;
 
 void efi_sync_low_kernel_mappings(void) {}
 void __init efi_dump_pagetable(void) {}
@@ -61,8 +60,6 @@ void __init efi_call_phys_prolog(void)
 {
 	struct desc_ptr gdt_descr;
 
-	local_irq_save(efi_rt_eflags);
-
 	load_cr3(initial_page_table);
 	__flush_tlb_all();
 
@@ -81,8 +78,6 @@ void __init efi_call_phys_epilog(void)
 
 	load_cr3(swapper_pg_dir);
 	__flush_tlb_all();
-
-	local_irq_restore(efi_rt_eflags);
 }
 
 void __init efi_runtime_mkexec(void)

arch/x86/platform/efi/efi_64.c

@@ -42,7 +42,6 @@
 #include <asm/time.h>
 
 static pgd_t *save_pgd __initdata;
-static unsigned long efi_flags __initdata;
 
 /*
  * We allocate runtime services regions bottom-up, starting from -4G, i.e.
@@ -88,7 +87,6 @@ void __init efi_call_phys_prolog(void)
 		return;
 
 	early_code_mapping_set_exec(1);
-	local_irq_save(efi_flags);
 
 	n_pgds = DIV_ROUND_UP((max_pfn << PAGE_SHIFT), PGDIR_SIZE);
 	save_pgd = kmalloc(n_pgds * sizeof(pgd_t), GFP_KERNEL);
@@ -116,7 +114,6 @@ void __init efi_call_phys_epilog(void)
 		set_pgd(pgd_offset_k(pgd * PGDIR_SIZE), save_pgd[pgd]);
 	kfree(save_pgd);
 	__flush_tlb_all();
-	local_irq_restore(efi_flags);
 	early_code_mapping_set_exec(0);
 }