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Date: Tue, 5 Aug 2014 11:13:53 -0700 From: Greg Kroah-Hartman <gregkh@...uxfoundation.org> To: linux-kernel@...r.kernel.org Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>, stable@...r.kernel.org, Max Filippov <jcmvbkbc@...il.com> Subject: [PATCH 3.15 39/42] xtensa: add fixup for double exception raised in window overflow 3.15-stable review patch. If anyone has any objections, please let me know. ------------------ From: Max Filippov <jcmvbkbc@...il.com> commit 17290231df16eeee5dfc198dbf5ee4b419996dcd upstream. There are two FIXMEs in the double exception handler 'for the extremely unlikely case'. This case gets hit by gcc during kernel build once in a few hours, resulting in an unrecoverable exception condition. Provide missing fixup routine to handle this case. Double exception literals now need 8 more bytes, add them to the linker script. Also replace bbsi instructions with bbsi.l as we're branching depending on 8th and 7th LSB-based bits of exception address. This may be tested by adding the explicit DTLB invalidation to window overflow handlers, like the following: # --- a/arch/xtensa/kernel/vectors.S # +++ b/arch/xtensa/kernel/vectors.S # @@ -592,6 +592,14 @@ ENDPROC(_WindowUnderflow4) # ENTRY_ALIGN64(_WindowOverflow8) # # s32e a0, a9, -16 # + bbsi.l a9, 31, 1f # + rsr a0, ccount # + bbsi.l a0, 4, 1f # + pdtlb a0, a9 # + idtlb a0 # + movi a0, 9 # + idtlb a0 # +1: # l32e a0, a1, -12 # s32e a2, a9, -8 # s32e a1, a9, -12 Signed-off-by: Max Filippov <jcmvbkbc@...il.com> Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org> --- arch/xtensa/kernel/vectors.S | 158 +++++++++++++++++++++++++++++++++------ arch/xtensa/kernel/vmlinux.lds.S | 4 2 files changed, 138 insertions(+), 24 deletions(-) --- a/arch/xtensa/kernel/vectors.S +++ b/arch/xtensa/kernel/vectors.S @@ -376,38 +376,42 @@ _DoubleExceptionVector_WindowOverflow: beqz a2, 1f # if at start of vector, don't restore addi a0, a0, -128 - bbsi a0, 8, 1f # don't restore except for overflow 8 and 12 - bbsi a0, 7, 2f + bbsi.l a0, 8, 1f # don't restore except for overflow 8 and 12 + + /* + * This fixup handler is for the extremely unlikely case where the + * overflow handler's reference thru a0 gets a hardware TLB refill + * that bumps out the (distinct, aliasing) TLB entry that mapped its + * prior references thru a9/a13, and where our reference now thru + * a9/a13 gets a 2nd-level miss exception (not hardware TLB refill). + */ + movi a2, window_overflow_restore_a0_fixup + s32i a2, a3, EXC_TABLE_FIXUP + l32i a2, a3, EXC_TABLE_DOUBLE_SAVE + xsr a3, excsave1 + + bbsi.l a0, 7, 2f /* * Restore a0 as saved by _WindowOverflow8(). - * - * FIXME: we really need a fixup handler for this L32E, - * for the extremely unlikely case where the overflow handler's - * reference thru a0 gets a hardware TLB refill that bumps out - * the (distinct, aliasing) TLB entry that mapped its prior - * references thru a9, and where our reference now thru a9 - * gets a 2nd-level miss exception (not hardware TLB refill). */ - l32e a2, a9, -16 - wsr a2, depc # replace the saved a0 - j 1f + l32e a0, a9, -16 + wsr a0, depc # replace the saved a0 + j 3f 2: /* * Restore a0 as saved by _WindowOverflow12(). - * - * FIXME: we really need a fixup handler for this L32E, - * for the extremely unlikely case where the overflow handler's - * reference thru a0 gets a hardware TLB refill that bumps out - * the (distinct, aliasing) TLB entry that mapped its prior - * references thru a13, and where our reference now thru a13 - * gets a 2nd-level miss exception (not hardware TLB refill). */ - l32e a2, a13, -16 - wsr a2, depc # replace the saved a0 + l32e a0, a13, -16 + wsr a0, depc # replace the saved a0 +3: + xsr a3, excsave1 + movi a0, 0 + s32i a0, a3, EXC_TABLE_FIXUP + s32i a2, a3, EXC_TABLE_DOUBLE_SAVE 1: /* * Restore WindowBase while leaving all address registers restored. @@ -449,6 +453,7 @@ _DoubleExceptionVector_WindowOverflow: s32i a0, a2, PT_DEPC +_DoubleExceptionVector_handle_exception: addx4 a0, a0, a3 l32i a0, a0, EXC_TABLE_FAST_USER xsr a3, excsave1 @@ -464,11 +469,120 @@ _DoubleExceptionVector_WindowOverflow: rotw -3 j 1b - .end literal_prefix ENDPROC(_DoubleExceptionVector) /* + * Fixup handler for TLB miss in double exception handler for window owerflow. + * We get here with windowbase set to the window that was being spilled and + * a0 trashed. a0 bit 7 determines if this is a call8 (bit clear) or call12 + * (bit set) window. + * + * We do the following here: + * - go to the original window retaining a0 value; + * - set up exception stack to return back to appropriate a0 restore code + * (we'll need to rotate window back and there's no place to save this + * information, use different return address for that); + * - handle the exception; + * - go to the window that was being spilled; + * - set up window_overflow_restore_a0_fixup as a fixup routine; + * - reload a0; + * - restore the original window; + * - reset the default fixup routine; + * - return to user. By the time we get to this fixup handler all information + * about the conditions of the original double exception that happened in + * the window overflow handler is lost, so we just return to userspace to + * retry overflow from start. + * + * a0: value of depc, original value in depc + * a2: trashed, original value in EXC_TABLE_DOUBLE_SAVE + * a3: exctable, original value in excsave1 + */ + +ENTRY(window_overflow_restore_a0_fixup) + + rsr a0, ps + extui a0, a0, PS_OWB_SHIFT, PS_OWB_WIDTH + rsr a2, windowbase + sub a0, a2, a0 + extui a0, a0, 0, 3 + l32i a2, a3, EXC_TABLE_DOUBLE_SAVE + xsr a3, excsave1 + + _beqi a0, 1, .Lhandle_1 + _beqi a0, 3, .Lhandle_3 + + .macro overflow_fixup_handle_exception_pane n + + rsr a0, depc + rotw -\n + + xsr a3, excsave1 + wsr a2, depc + l32i a2, a3, EXC_TABLE_KSTK + s32i a0, a2, PT_AREG0 + + movi a0, .Lrestore_\n + s32i a0, a2, PT_DEPC + rsr a0, exccause + j _DoubleExceptionVector_handle_exception + + .endm + + overflow_fixup_handle_exception_pane 2 +.Lhandle_1: + overflow_fixup_handle_exception_pane 1 +.Lhandle_3: + overflow_fixup_handle_exception_pane 3 + + .macro overflow_fixup_restore_a0_pane n + + rotw \n + /* Need to preserve a0 value here to be able to handle exception + * that may occur on a0 reload from stack. It may occur because + * TLB miss handler may not be atomic and pointer to page table + * may be lost before we get here. There are no free registers, + * so we need to use EXC_TABLE_DOUBLE_SAVE area. + */ + xsr a3, excsave1 + s32i a2, a3, EXC_TABLE_DOUBLE_SAVE + movi a2, window_overflow_restore_a0_fixup + s32i a2, a3, EXC_TABLE_FIXUP + l32i a2, a3, EXC_TABLE_DOUBLE_SAVE + xsr a3, excsave1 + bbsi.l a0, 7, 1f + l32e a0, a9, -16 + j 2f +1: + l32e a0, a13, -16 +2: + rotw -\n + + .endm + +.Lrestore_2: + overflow_fixup_restore_a0_pane 2 + +.Lset_default_fixup: + xsr a3, excsave1 + s32i a2, a3, EXC_TABLE_DOUBLE_SAVE + movi a2, 0 + s32i a2, a3, EXC_TABLE_FIXUP + l32i a2, a3, EXC_TABLE_DOUBLE_SAVE + xsr a3, excsave1 + rfe + +.Lrestore_1: + overflow_fixup_restore_a0_pane 1 + j .Lset_default_fixup +.Lrestore_3: + overflow_fixup_restore_a0_pane 3 + j .Lset_default_fixup + +ENDPROC(window_overflow_restore_a0_fixup) + + .end literal_prefix +/* * Debug interrupt vector * * There is not much space here, so simply jump to another handler. --- a/arch/xtensa/kernel/vmlinux.lds.S +++ b/arch/xtensa/kernel/vmlinux.lds.S @@ -269,13 +269,13 @@ SECTIONS .UserExceptionVector.literal) SECTION_VECTOR (_DoubleExceptionVector_literal, .DoubleExceptionVector.literal, - DOUBLEEXC_VECTOR_VADDR - 16, + DOUBLEEXC_VECTOR_VADDR - 40, SIZEOF(.UserExceptionVector.text), .UserExceptionVector.text) SECTION_VECTOR (_DoubleExceptionVector_text, .DoubleExceptionVector.text, DOUBLEEXC_VECTOR_VADDR, - 32, + 40, .DoubleExceptionVector.literal) . = (LOADADDR( .DoubleExceptionVector.text ) + SIZEOF( .DoubleExceptionVector.text ) + 3) & ~ 3; -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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