- Fix build error on RHEL where -Werror=maybe-uninitialized is set.

- Restore the firmware's IDT when calling EFI boot services and before
 ExitBootServices() has been called. This fixes a boot failure on what
 appears to be a tablet with 32-bit UEFI running a 64-bit kernel.
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Merge tag 'x86_urgent_for_v5.14' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

Pull x86 fixes from Borislav Petkov:

 - Fix build error on RHEL where -Werror=maybe-uninitialized is set.

 - Restore the firmware's IDT when calling EFI boot services and before
   ExitBootServices() has been called. This fixes a boot failure on what
   appears to be a tablet with 32-bit UEFI running a 64-bit kernel.

* tag 'x86_urgent_for_v5.14' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  x86/resctrl: Fix a maybe-uninitialized build warning treated as error
  x86/efi: Restore Firmware IDT before calling ExitBootServices()

arch/x86/boot/compressed/efi_thunk_64.S

@@ -5,9 +5,8 @@
  * Early support for invoking 32-bit EFI services from a 64-bit kernel.
  *
  * Because this thunking occurs before ExitBootServices() we have to
- * restore the firmware's 32-bit GDT before we make EFI service calls,
- * since the firmware's 32-bit IDT is still currently installed and it
- * needs to be able to service interrupts.
+ * restore the firmware's 32-bit GDT and IDT before we make EFI service
+ * calls.
  *
  * On the plus side, we don't have to worry about mangling 64-bit
  * addresses into 32-bits because we're executing with an identity
@@ -39,7 +38,7 @@ SYM_FUNC_START(__efi64_thunk)
 	/*
 	 * Convert x86-64 ABI params to i386 ABI
 	 */
-	subq	$32, %rsp
+	subq	$64, %rsp
 	movl	%esi, 0x0(%rsp)
 	movl	%edx, 0x4(%rsp)
 	movl	%ecx, 0x8(%rsp)
@@ -49,14 +48,19 @@ SYM_FUNC_START(__efi64_thunk)
 	leaq	0x14(%rsp), %rbx
 	sgdt	(%rbx)
 
+	addq	$16, %rbx
+	sidt	(%rbx)
+
 	/*
-	 * Switch to gdt with 32-bit segments. This is the firmware GDT
-	 * that was installed when the kernel started executing. This
-	 * pointer was saved at the EFI stub entry point in head_64.S.
+	 * Switch to IDT and GDT with 32-bit segments. This is the firmware GDT
+	 * and IDT that was installed when the kernel started executing. The
+	 * pointers were saved at the EFI stub entry point in head_64.S.
 	 *
 	 * Pass the saved DS selector to the 32-bit code, and use far return to
 	 * restore the saved CS selector.
 	 */
+	leaq	efi32_boot_idt(%rip), %rax
+	lidt	(%rax)
 	leaq	efi32_boot_gdt(%rip), %rax
 	lgdt	(%rax)
 
@@ -67,7 +71,7 @@ SYM_FUNC_START(__efi64_thunk)
 	pushq	%rax
 	lretq
 
-1:	addq	$32, %rsp
+1:	addq	$64, %rsp
 	movq	%rdi, %rax
 
 	pop	%rbx
@@ -128,10 +132,13 @@ SYM_FUNC_START_LOCAL(efi_enter32)
 
 	/*
 	 * Some firmware will return with interrupts enabled. Be sure to
-	 * disable them before we switch GDTs.
+	 * disable them before we switch GDTs and IDTs.
 	 */
 	cli
 
+	lidtl	(%ebx)
+	subl	$16, %ebx
+
 	lgdtl	(%ebx)
 
 	movl	%cr4, %eax
@@ -166,6 +173,11 @@ SYM_DATA_START(efi32_boot_gdt)
 	.quad	0
 SYM_DATA_END(efi32_boot_gdt)
 
+SYM_DATA_START(efi32_boot_idt)
+	.word	0
+	.quad	0
+SYM_DATA_END(efi32_boot_idt)
+
 SYM_DATA_START(efi32_boot_cs)
 	.word	0
 SYM_DATA_END(efi32_boot_cs)

arch/x86/boot/compressed/head_64.S

@@ -319,6 +319,9 @@ SYM_INNER_LABEL(efi32_pe_stub_entry, SYM_L_LOCAL)
 	movw	%cs, rva(efi32_boot_cs)(%ebp)
 	movw	%ds, rva(efi32_boot_ds)(%ebp)
 
+	/* Store firmware IDT descriptor */
+	sidtl	rva(efi32_boot_idt)(%ebp)
+
 	/* Disable paging */
 	movl	%cr0, %eax
 	btrl	$X86_CR0_PG_BIT, %eax

arch/x86/kernel/cpu/resctrl/monitor.c

@@ -304,6 +304,12 @@ static u64 __mon_event_count(u32 rmid, struct rmid_read *rr)
 	case QOS_L3_MBM_LOCAL_EVENT_ID:
 		m = &rr->d->mbm_local[rmid];
 		break;
+	default:
+		/*
+		 * Code would never reach here because an invalid
+		 * event id would fail the __rmid_read.
+		 */
+		return RMID_VAL_ERROR;
 	}
 
 	if (rr->first) {