Messages in this thread | | | Subject | Re: [PATCH V15 06/11] acpi: apei: handle SEA notification type for ARMv8 | From | "Baicar, Tyler" <> | Date | Mon, 8 May 2017 13:59:37 -0600 |
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On 5/8/2017 11:28 AM, James Morse wrote: > Hi Tyler, > > On 19/04/17 00:05, Tyler Baicar wrote: >> ARM APEI extension proposal added SEA (Synchronous External Abort) >> notification type for ARMv8. >> Add a new GHES error source handling function for SEA. If an error >> source's notification type is SEA, then this function can be registered >> into the SEA exception handler. That way GHES will parse and report >> SEA exceptions when they occur. >> An SEA can interrupt code that had interrupts masked and is treated as >> an NMI. To aid this the page of address space for mapping APEI buffers >> while in_nmi() is always reserved, and ghes_ioremap_pfn_nmi() is >> changed to use the helper methods to find the prot_t to map with in >> the same way as ghes_ioremap_pfn_irq(). >> diff --git a/arch/arm64/mm/fault.c b/arch/arm64/mm/fault.c >> index b74d8b7..10013ff 100644 >> --- a/arch/arm64/mm/fault.c >> +++ b/arch/arm64/mm/fault.c >> @@ -518,6 +520,17 @@ static int do_sea(unsigned long addr, unsigned int esr, struct pt_regs *regs) >> pr_err("Synchronous External Abort: %s (0x%08x) at 0x%016lx\n", >> inf->name, esr, addr); >> >> + /* >> + * Synchronous aborts may interrupt code which had interrupts masked. >> + * Before calling out into the wider kernel tell the interested >> + * subsystems. >> + */ >> + if (IS_ENABLED(CONFIG_ACPI_APEI_SEA)) { >> + nmi_enter(); >> + ghes_notify_sea(); >> + nmi_exit(); >> + } >> + >> info.si_signo = SIGBUS; >> info.si_errno = 0; >> info.si_code = 0; > > I was tidying up the masking/unmasking in entry.S, something I wasn't aware of > that leads to a bug: > entry.S will unmask interrupts for instruction/data aborts that came from a > context with interrupts enabled. This makes sense for get_user() and friends... > For do_sea() we pull nmi_enter() as this can interrupt interrupts-masked code, > such as APEI, but if we end up in here with interrupts unmasked we can take an > IRQ from this 'NMI' context, which will inherit the in_nmi() and could lead to > the deadlock we were originally trying to avoid. > > Teaching entry.S to spot external aborts is messy. I think the two choices are > to either mask interrupts when calling nmi_enter() (as these things should be > mutually exclusive), or to conditionally call nmi_enter() based on > interrupts_enabled(regs). I prefer the second one as it matches the notify_sea() > while interruptible that happens when KVM takes one of these. Hello James,
So it would need to be like this?
if(interrupts_enabled(regs)) nmi_enter(); ghes_notify_sea(); if(interrupts_enabled(regs)) nmi_exit();
Thanks, Tyler
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