From mboxrd@z Thu Jan 1 00:00:00 1970 From: Takao Indoh Date: Mon, 26 Oct 2009 22:15:22 +0000 Subject: Re: why ms->pmsa_xip is used? Message-Id: <1CA5689CF5578indou.takao@jp.fujitsu.com> List-Id: References: In-Reply-To: MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: linux-ia64@vger.kernel.org On Wed, 21 Oct 2009 10:53:18 +1100, Keith Owens wrote: >On Tue, 20 Oct 2009 15:25:23 -0400, >Takao Indoh wrote: >>Hi, >> >>I have a question about how to restore cr_{iip,ipsr,ifs} register >>in the INIT handler. >> >>This is a part of ia64_mca_modify_original_stack(). >> >> /* If ipsr.ic then use pmsa_{iip,ipsr,ifs}, else use >> * pmsa_{xip,xpsr,xfs} >> */ >> if (ia64_psr(regs)->ic) { >> old_regs->cr_iip = ms->pmsa_iip; >> old_regs->cr_ipsr = ms->pmsa_ipsr; >> old_regs->cr_ifs = ms->pmsa_ifs; >> } else { >> old_regs->cr_iip = ms->pmsa_xip; >> old_regs->cr_ipsr = ms->pmsa_xpsr; >> old_regs->cr_ifs = ms->pmsa_xfs; >> } >> >>Does anybody know why ms->pmsa_{xip,xpsr,xfs} are used instead of >>ms->pmsa_{iip,ipsr,ifs} when PSR.ic is 0? > >That's my code. Take a look at "OS Machine Check Recovery on >Itanium Based Systems", http://download.intel.com/design/itanium/320482.pdf. >Section 2.5, Min-State Save Area I-Resources and X-Resources. > > On an interruption (either PAL-based or IVA-based), the processor > stores architectural state to the I-resources (IIP, IPSR, IIM, and > IFS). During interrupt handling, interrupt collection is masked with > PSR.ic = 0, but PSR.mc = 1 and machine check aborts can be delivered. > > To permit error recovery when PSR.ic = 0, current Itanium processor > implementations provide optional X-resources (XIP, XPSR, XFS, XR0 - > XR4). (Availability of X-resources on a processor implementation can > be identified using PAL_PROC_GET_FEATURE bits 41 and 42.) If an MCA > occurs while PSR.ic = 0, the I-resources are saved to the X-resources > and the processor state at the time of the MCA is stored to the > I-resources. > > The PAL MCA handler will copy I-resources and X-resources to the > min-state save area. SAL_CHECK saves the min-state save area to > NVRAM in the processor error section and provides the error record to > OS_MCA when SAL_GET_STATE_INFO is called. OS_MCA can determine if an > interruption was in progress at the time of the MCA by examining > IPSR.ic. If IPSR.ic = 0, the X-resources provide information about > the processor state at the time the original interruption was taken. > If IPSR.ic = 1, the X-resources are undefined. > >>What we want to do here is to modify the original stack so it looks as >>if it's interrupted by INIT, right? In my understainding, if PSR.ic is 0, >>pmsa_iip has the value of IP register and pmsa_xip has the value of IIP >>register. In other words, the value of pmsa_iip is where INIT handler >>returns to, and the value of pmsa_xip is where interruption handler (not >>INIT handler) returns to. So, to create pt_regs which has the state at >>the time of interrupt by INIT, ms->pmsa_iip should be used when PSR.ic >>is 0, I think. My understanding is correct? > >According to the extract above, ia64 MCA handler should always be using >pmsa_iip, it is meant to be the IP at the time of the MCA. I vaguely >remember a test where I created an MCA with interrupts disabled and >finding that I needed to use pmsa_xip, but that was a long time ago and >I could be remembering it wrong. I no longer have access to ia64 >equipment so I cannot test this. If your tests show that pmsa_iip is >valid when psr.ic = 0 then please change the code. To confirm this, I inserted debug code like this: diff -Nurp a/arch/ia64/kernel/irq_ia64.c b/arch/ia64/kernel/irq_ia64.c --- a/arch/ia64/kernel/irq_ia64.c 2009-10-22 12:28:07.000000000 -0400 +++ b/arch/ia64/kernel/irq_ia64.c 2009-10-23 11:32:03.000000000 -0400 @@ -453,7 +453,12 @@ ia64_handle_irq (ia64_vector vector, str { struct pt_regs *old_regs = set_irq_regs(regs); unsigned long saved_tpr; + extern int debug; + if (debug) { + ia64_clear_ic(); + while(1); + } #if IRQ_DEBUG { unsigned long bsp, sp; After kernel hung, I sent INIT and took a vmcore by kdump to check a value of pmsa_iip and pmsa_xip. Here is the result. CPU0 pmsa_iip = 0xa000000100013270 pmsa_xip = 0xa000000100183800 CPU1 pmsa_iip = 0xa000000100013270 pmsa_xip = 0xa0000001006c3430 <_spin_unlock_irqrestore+48> CPU2 pmsa_iip = 0xa000000100013270 pmsa_xip = 0xa00000010032ab20 <__copy_user+288> CPU3 pmsa_iip = 0xa000000100013270 pmsa_xip = 0xa00000010010dff0 CPU4 pmsa_iip = 0xa000000100013270 pmsa_xip = 0x4000000000003180 CPU5 pmsa_iip = 0xa000000100013270 pmsa_xip = 0xa000000000010720 <__kernel_syscall_via_break> CPU6 pmsa_iip = 0xa000000100013270 pmsa_xip = 0xa00000010028e460 CPU7 pmsa_iip = 0xa000000100013270 pmsa_xip = 0xa000000100194ba0 As Intel manual says, it seems that pmsa_iip has a value of ip register where INIT interrupted when psr.ic is 0. Ok, I'll make a patch so that pmsa_iip is used irrespective of a value of psr.ic. Please let me know if I need to confirm something else before I make a patch. Thanks, Takao Indoh