>From 61a869c6b8d97c761a7ba60ea316ae6b83e01ef1 Mon Sep 17 00:00:00 2001 From: Kevin D. Kissell <kevink@xxxxxxxxxxxxx> Date: Tue, 9 Sep 2008 21:35:01 +0200 Subject: [PATCH] Close tiny holes in the SMTC IPI replay system. Signed-off-by: Kevin D. Kissell <kevink@xxxxxxxxxxxxx> --- arch/mips/kernel/entry.S | 10 +++--- include/asm-mips/stackframe.h | 72 ++++++++++++++++++++++++++++++++++------ 2 files changed, 66 insertions(+), 16 deletions(-) diff --git a/arch/mips/kernel/entry.S b/arch/mips/kernel/entry.S index e29598a..ffa3310 100644 --- a/arch/mips/kernel/entry.S +++ b/arch/mips/kernel/entry.S @@ -79,11 +79,6 @@ FEXPORT(syscall_exit) FEXPORT(restore_all) # restore full frame #ifdef CONFIG_MIPS_MT_SMTC -/* Detect and execute deferred IPI "interrupts" */ - LONG_L s0, TI_REGS($28) - LONG_S sp, TI_REGS($28) - jal deferred_smtc_ipi - LONG_S s0, TI_REGS($28) #ifdef CONFIG_MIPS_MT_SMTC_IM_BACKSTOP /* Re-arm any temporarily masked interrupts not explicitly "acked" */ mfc0 v0, CP0_TCSTATUS @@ -112,6 +107,11 @@ FEXPORT(restore_all) # restore full frame xor t0, t0, t3 mtc0 t0, CP0_TCCONTEXT #endif /* CONFIG_MIPS_MT_SMTC_IM_BACKSTOP */ +/* Detect and execute deferred IPI "interrupts" */ + LONG_L s0, TI_REGS($28) + LONG_S sp, TI_REGS($28) + jal deferred_smtc_ipi + LONG_S s0, TI_REGS($28) #endif /* CONFIG_MIPS_MT_SMTC */ .set noat RESTORE_TEMP diff --git a/include/asm-mips/stackframe.h b/include/asm-mips/stackframe.h index 051e1af..4c37c4e 100644 --- a/include/asm-mips/stackframe.h +++ b/include/asm-mips/stackframe.h @@ -297,14 +297,31 @@ #ifdef CONFIG_MIPS_MT_SMTC .set mips32r2 /* - * This may not really be necessary if ints are already - * inhibited here. + * We need to make sure the read-modify-write + * of Status below isn't perturbed by an interrupt + * or cross-TC access, so we need to do at least a DMT, + * protected by an interrupt-inhibit. But setting IXMT + * also creates a few-cycle window where an IPI could + * be queued and not be detected before potentially + * returning to a WAIT or user-mode loop. It must be + * replayed. + * + * We're in the middle of a context switch, and + * we can't dispatch it directly without trashing + * some registers, so we'll try to detect this unlikely + * case and program a software interrupt in the VPE, + * as would be done for a cross-VPE IPI. To accomodate + * the handling of that case, we're doing a DVPE instead + * of just a DMT here to protect against other threads. + * This is a lot of cruft to cover a tiny window. + * If you can find a better design, implement it! + * */ mfc0 v0, CP0_TCSTATUS ori v0, TCSTATUS_IXMT mtc0 v0, CP0_TCSTATUS _ehb - DMT 5 # dmt a1 + DVPE 5 # dvpe a1 jal mips_ihb #endif /* CONFIG_MIPS_MT_SMTC */ mfc0 a0, CP0_STATUS @@ -325,17 +342,50 @@ */ LONG_L v1, PT_TCSTATUS(sp) _ehb - mfc0 v0, CP0_TCSTATUS + mfc0 a0, CP0_TCSTATUS andi v1, TCSTATUS_IXMT - /* We know that TCStatua.IXMT should be set from above */ - xori v0, v0, TCSTATUS_IXMT - or v0, v0, v1 - mtc0 v0, CP0_TCSTATUS - _ehb - andi a1, a1, VPECONTROL_TE + bnez v1, 0f + +/* + * We'd like to detect any IPIs queued in the tiny window + * above and request an software interrupt to service them + * when we ERET. + * + * Computing the offset into the IPIQ array of the executing + * TC's IPI queue in-line would be tedious. We use part of + * the TCContext register to hold 16 bits of offset that we + * can add in-line to find the queue head. + */ + mfc0 v0, CP0_TCCONTEXT + la a2, IPIQ + srl v0, v0, 16 + addu a2, a2, v0 + LONG_L v0, 0(a2) + beqz v0, 0f +/* + * If we have a queue, provoke dispatch within the VPE by setting C_SW1 + */ + mfc0 v0, CP0_CAUSE + ori v0, v0, C_SW1 + mtc0 v0, CP0_CAUSE +0: + /* + * This test should really never branch but + * let's be prudent here. Having atomized + * the shared register modifications, we can + * now EVPE, and must do so before interrupts + * are potentially re-enabled. + */ + andi a1, a1, MVPCONTROL_EVP beqz a1, 1f - emt + evpe 1: + /* We know that TCStatua.IXMT should be set from above */ + xori a0, a0, TCSTATUS_IXMT + or a0, a0, v1 + mtc0 a0, CP0_TCSTATUS + _ehb + .set mips0 #endif /* CONFIG_MIPS_MT_SMTC */ LONG_L v1, PT_EPC(sp) -- 1.5.3.3
