A couple of x86 fixes which missed rc1 due to my stupidity:

- Drop lazy TLB mode before switching to the temporary address space for
     text patching. text_poke() switches to the temporary mm which clears
     the lazy mode and restores the original mm afterwards. Due to clearing
     lazy mode this might restore a already dead mm if exit_mmap() runs in
     parallel on another CPU.
 
   - Document the x32 syscall design fail vs. syscall numbers 512-547
     properly.
 
   - Fix the ORC unwinder to handle the inactive task frame correctly. This
     was unearthed due to the slightly different code generation of GCC10.
 
   - Use an up to date screen_info for the boot params of kexec instead of
     the possibly stale and invalid version which happened to be valid when
     the kexec kernel was loaded.
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Merge tag 'x86-urgent-2020-10-27' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

Pull x86 fixes from Thomas Gleixner:
 "A couple of x86 fixes which missed rc1 due to my stupidity:

   - Drop lazy TLB mode before switching to the temporary address space
     for text patching.

     text_poke() switches to the temporary mm which clears the lazy mode
     and restores the original mm afterwards. Due to clearing lazy mode
     this might restore a already dead mm if exit_mmap() runs in
     parallel on another CPU.

   - Document the x32 syscall design fail vs. syscall numbers 512-547
     properly.

   - Fix the ORC unwinder to handle the inactive task frame correctly.

     This was unearthed due to the slightly different code generation of
     gcc-10.

   - Use an up to date screen_info for the boot params of kexec instead
     of the possibly stale and invalid version which happened to be
     valid when the kexec kernel was loaded"

* tag 'x86-urgent-2020-10-27' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  x86/alternative: Don't call text_poke() in lazy TLB mode
  x86/syscalls: Document the fact that syscalls 512-547 are a legacy mistake
  x86/unwind/orc: Fix inactive tasks with stack pointer in %sp on GCC 10 compiled kernels
  hyperv_fb: Update screen_info after removing old framebuffer
  x86/kexec: Use up-to-dated screen_info copy to fill boot params

arch/x86/entry/syscalls/syscall_64.tbl

@@ -364,10 +364,10 @@
 440	common	process_madvise		sys_process_madvise
 
 #
-# x32-specific system call numbers start at 512 to avoid cache impact
-# for native 64-bit operation. The __x32_compat_sys stubs are created
-# on-the-fly for compat_sys_*() compatibility system calls if X86_X32
-# is defined.
+# Due to a historical design error, certain syscalls are numbered differently
+# in x32 as compared to native x86_64.  These syscalls have numbers 512-547.
+# Do not add new syscalls to this range.  Numbers 548 and above are available
+# for non-x32 use.
 #
 512	x32	rt_sigaction		compat_sys_rt_sigaction
 513	x32	rt_sigreturn		compat_sys_x32_rt_sigreturn
@@ -405,3 +405,5 @@
 545	x32	execveat		compat_sys_execveat
 546	x32	preadv2			compat_sys_preadv64v2
 547	x32	pwritev2		compat_sys_pwritev64v2
+# This is the end of the legacy x32 range.  Numbers 548 and above are
+# not special and are not to be used for x32-specific syscalls.

arch/x86/kernel/alternative.c

@@ -807,6 +807,15 @@ static inline temp_mm_state_t use_temporary_mm(struct mm_struct *mm)
 	temp_mm_state_t temp_state;
 
 	lockdep_assert_irqs_disabled();
+
+	/*
+	 * Make sure not to be in TLB lazy mode, as otherwise we'll end up
+	 * with a stale address space WITHOUT being in lazy mode after
+	 * restoring the previous mm.
+	 */
+	if (this_cpu_read(cpu_tlbstate.is_lazy))
+		leave_mm(smp_processor_id());
+
 	temp_state.mm = this_cpu_read(cpu_tlbstate.loaded_mm);
 	switch_mm_irqs_off(NULL, mm, current);
 

arch/x86/kernel/kexec-bzimage64.c

@@ -200,8 +200,7 @@ setup_boot_parameters(struct kimage *image, struct boot_params *params,
 	params->hdr.hardware_subarch = boot_params.hdr.hardware_subarch;
 
 	/* Copying screen_info will do? */
-	memcpy(&params->screen_info, &boot_params.screen_info,
-				sizeof(struct screen_info));
+	memcpy(&params->screen_info, &screen_info, sizeof(struct screen_info));
 
 	/* Fill in memsize later */
 	params->screen_info.ext_mem_k = 0;

arch/x86/kernel/unwind_orc.c

@@ -321,19 +321,12 @@ EXPORT_SYMBOL_GPL(unwind_get_return_address);
 
 unsigned long *unwind_get_return_address_ptr(struct unwind_state *state)
 {
-	struct task_struct *task = state->task;
-
 	if (unwind_done(state))
 		return NULL;
 
 	if (state->regs)
 		return &state->regs->ip;
 
-	if (task != current && state->sp == task->thread.sp) {
-		struct inactive_task_frame *frame = (void *)task->thread.sp;
-		return &frame->ret_addr;
-	}
-
 	if (state->sp)
 		return (unsigned long *)state->sp - 1;
 
@@ -663,7 +656,7 @@ void __unwind_start(struct unwind_state *state, struct task_struct *task,
 	} else {
 		struct inactive_task_frame *frame = (void *)task->thread.sp;
 
-		state->sp = task->thread.sp;
+		state->sp = task->thread.sp + sizeof(*frame);
 		state->bp = READ_ONCE_NOCHECK(frame->bp);
 		state->ip = READ_ONCE_NOCHECK(frame->ret_addr);
 		state->signal = (void *)state->ip == ret_from_fork;

drivers/video/fbdev/hyperv_fb.c

@@ -1114,8 +1114,15 @@ static int hvfb_getmem(struct hv_device *hdev, struct fb_info *info)
 getmem_done:
 	remove_conflicting_framebuffers(info->apertures,
 					KBUILD_MODNAME, false);
-	if (!gen2vm)
+
+	if (gen2vm) {
+		/* framebuffer is reallocated, clear screen_info to avoid misuse from kexec */
+		screen_info.lfb_size = 0;
+		screen_info.lfb_base = 0;
+		screen_info.orig_video_isVGA = 0;
+	} else {
 		pci_dev_put(pdev);
+	}
 	kfree(info->apertures);
 
 	return 0;