Merge tag 'x86_cpu_for_7.1-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

Pull x86 cpu updates from Dave Hansen:

 - Complete LASS enabling: deal with vsyscall and EFI

   The existing Linear Address Space Separation (LASS) support punted
   on support for common EFI and vsyscall configs. Complete the
   implementation by supporting EFI and vsyscall=xonly.

 - Clean up CPUID usage in newer Intel "avs" audio driver and update the
   x86-cpuid-db file

* tag 'x86_cpu_for_7.1-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  tools/x86/kcpuid: Update bitfields to x86-cpuid-db v3.0
  ASoC: Intel: avs: Include CPUID header at file scope
  ASoC: Intel: avs: Check maximum valid CPUID leaf
  x86/cpu: Remove LASS restriction on vsyscall emulation
  x86/vsyscall: Disable LASS if vsyscall mode is set to EMULATE
  x86/vsyscall: Restore vsyscall=xonly mode under LASS
  x86/traps: Consolidate user fixups in the #GP handler
  x86/vsyscall: Reorganize the page fault emulation code
  x86/cpu: Remove LASS restriction on EFI
  x86/efi: Disable LASS while executing runtime services
  x86/cpu: Defer LASS enabling until userspace comes up

1 files changed, 35 insertions, 0 deletions

diff --git a/arch/x86/platform/efi/efi_64.c b/arch/x86/platform/efi/efi_64.c
index b4409df2105a..5861008eab22 100644
--- a/arch/x86/platform/efi/efi_64.c
+++ b/arch/x86/platform/efi/efi_64.c
@@ -55,6 +55,7 @@
  */
 static u64 efi_va = EFI_VA_START;
 static struct mm_struct *efi_prev_mm;
+static unsigned long efi_cr4_lass;
 
 /*
  * We need our own copy of the higher levels of the page tables
@@ -443,16 +444,50 @@ static void efi_leave_mm(void)
 	unuse_temporary_mm(efi_prev_mm);
 }
 
+/*
+ * Toggle LASS to allow EFI to access any 1:1 mapped region in the lower
+ * half.
+ *
+ * Disable LASS only after switching to EFI-mm, as userspace is not
+ * mapped in it. Similar to EFI-mm, these rely on preemption being
+ * disabled and the calls being serialized.
+ */
+
+static void efi_disable_lass(void)
+{
+	if (!cpu_feature_enabled(X86_FEATURE_LASS))
+		return;
+
+	lockdep_assert_preemption_disabled();
+
+	/* Save current CR4.LASS state */
+	efi_cr4_lass = cr4_read_shadow() & X86_CR4_LASS;
+	cr4_clear_bits(efi_cr4_lass);
+}
+
+static void efi_enable_lass(void)
+{
+	if (!cpu_feature_enabled(X86_FEATURE_LASS))
+		return;
+
+	lockdep_assert_preemption_disabled();
+
+	/* Reprogram CR4.LASS only if it was set earlier */
+	cr4_set_bits(efi_cr4_lass);
+}
+
 void arch_efi_call_virt_setup(void)
 {
 	efi_sync_low_kernel_mappings();
 	efi_fpu_begin();
 	firmware_restrict_branch_speculation_start();
 	efi_enter_mm();
+	efi_disable_lass();
 }
 
 void arch_efi_call_virt_teardown(void)
 {
+	efi_enable_lass();
 	efi_leave_mm();
 	firmware_restrict_branch_speculation_end();
 	efi_fpu_end();