Merge branch 'x86-debug-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git...

[karo-tx-linux.git] / arch / x86 / kernel / entry_64.S

diff --git a/arch/x86/kernel/entry_64.S b/arch/x86/kernel/entry_64.S
index 54be36bf2620811502fea946514c013c575dd06a..734ebd1d3caabf0e0b058a1f8ed6aa947c1caf95 100644 (file)
--- a/arch/x86/kernel/entry_64.S
+++ b/arch/x86/kernel/entry_64.S
@@ -320,7 +320,7 @@ ENDPROC(native_usergs_sysret64)
        movq %rsp, %rsi
 
        leaq -RBP(%rsp),%rdi    /* arg1 for handler */
-       testl $3, CS(%rdi)
+       testl $3, CS-RBP(%rsi)
        je 1f
        SWAPGS
        /*
@@ -330,11 +330,10 @@ ENDPROC(native_usergs_sysret64)
         * moving irq_enter into assembly, which would be too much work)
         */
 1:     incl PER_CPU_VAR(irq_count)
-       jne 2f
-       mov PER_CPU_VAR(irq_stack_ptr),%rsp
+       cmovzq PER_CPU_VAR(irq_stack_ptr),%rsp
        CFI_DEF_CFA_REGISTER    rsi
 
-2:     /* Store previous stack value */
+       /* Store previous stack value */
        pushq %rsi
        CFI_ESCAPE      0x0f /* DW_CFA_def_cfa_expression */, 6, \
                        0x77 /* DW_OP_breg7 */, 0, \
@@ -1530,12 +1529,20 @@ ENTRY(nmi)
 
        /* Use %rdx as out temp variable throughout */
        pushq_cfi %rdx
+       CFI_REL_OFFSET rdx, 0
+
+       /*
+        * If %cs was not the kernel segment, then the NMI triggered in user
+        * space, which means it is definitely not nested.
+        */
+       cmpl $__KERNEL_CS, 16(%rsp)
+       jne first_nmi
 
        /*
         * Check the special variable on the stack to see if NMIs are
         * executing.
         */
-       cmp $1, -8(%rsp)
+       cmpl $1, -8(%rsp)
        je nested_nmi
 
        /*
@@ -1547,6 +1554,7 @@ ENTRY(nmi)
         */
        lea 6*8(%rsp), %rdx
        test_in_nmi rdx, 4*8(%rsp), nested_nmi, first_nmi
+       CFI_REMEMBER_STATE
 
 nested_nmi:
        /*
@@ -1578,10 +1586,12 @@ nested_nmi:
 
 nested_nmi_out:
        popq_cfi %rdx
+       CFI_RESTORE rdx
 
        /* No need to check faults here */
        INTERRUPT_RETURN
 
+       CFI_RESTORE_STATE
 first_nmi:
        /*
         * Because nested NMIs will use the pushed location that we
@@ -1613,10 +1623,15 @@ first_nmi:
         * | pt_regs                 |
         * +-------------------------+
         *
-        * The saved RIP is used to fix up the copied RIP that a nested
-        * NMI may zero out. The original stack frame and the temp storage
+        * The saved stack frame is used to fix up the copied stack frame
+        * that a nested NMI may change to make the interrupted NMI iret jump
+        * to the repeat_nmi. The original stack frame and the temp storage
         * is also used by nested NMIs and can not be trusted on exit.
         */
+       /* Do not pop rdx, nested NMIs will corrupt that part of the stack */
+       movq (%rsp), %rdx
+       CFI_RESTORE rdx
+
        /* Set the NMI executing variable on the stack. */
        pushq_cfi $1
 
@@ -1624,22 +1639,39 @@ first_nmi:
        .rept 5
        pushq_cfi 6*8(%rsp)
        .endr
+       CFI_DEF_CFA_OFFSET SS+8-RIP
+
+       /* Everything up to here is safe from nested NMIs */
+
+       /*
+        * If there was a nested NMI, the first NMI's iret will return
+        * here. But NMIs are still enabled and we can take another
+        * nested NMI. The nested NMI checks the interrupted RIP to see
+        * if it is between repeat_nmi and end_repeat_nmi, and if so
+        * it will just return, as we are about to repeat an NMI anyway.
+        * This makes it safe to copy to the stack frame that a nested
+        * NMI will update.
+        */
+repeat_nmi:
+       /*
+        * Update the stack variable to say we are still in NMI (the update
+        * is benign for the non-repeat case, where 1 was pushed just above
+        * to this very stack slot).
+        */
+       movq $1, 5*8(%rsp)
 
        /* Make another copy, this one may be modified by nested NMIs */
        .rept 5
        pushq_cfi 4*8(%rsp)
        .endr
-
-       /* Do not pop rdx, nested NMIs will corrupt it */
-       movq 11*8(%rsp), %rdx
+       CFI_DEF_CFA_OFFSET SS+8-RIP
+end_repeat_nmi:
 
        /*
         * Everything below this point can be preempted by a nested
-        * NMI if the first NMI took an exception. Repeated NMIs
-        * caused by an exception and nested NMI will start here, and
-        * can still be preempted by another NMI.
+        * NMI if the first NMI took an exception and reset our iret stack
+        * so that we repeat another NMI.
         */
-restart_nmi:
        pushq_cfi $-1           /* ORIG_RAX: no syscall to restart */
        subq $ORIG_RAX-R15, %rsp
        CFI_ADJUST_CFA_OFFSET ORIG_RAX-R15
@@ -1668,26 +1700,6 @@ nmi_restore:
        CFI_ENDPROC
 END(nmi)
 
-       /*
-        * If an NMI hit an iret because of an exception or breakpoint,
-        * it can lose its NMI context, and a nested NMI may come in.
-        * In that case, the nested NMI will change the preempted NMI's
-        * stack to jump to here when it does the final iret.
-        */
-repeat_nmi:
-       INTR_FRAME
-       /* Update the stack variable to say we are still in NMI */
-       movq $1, 5*8(%rsp)
-
-       /* copy the saved stack back to copy stack */
-       .rept 5
-       pushq_cfi 4*8(%rsp)
-       .endr
-
-       jmp restart_nmi
-       CFI_ENDPROC
-end_repeat_nmi:
-
 ENTRY(ignore_sysret)
        CFI_STARTPROC
        mov $-ENOSYS,%eax