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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