Hi Mark, James, Thanks the review. On 2018/6/1 0:51, James Morse wrote: > Hi Mark, Dongjiu Geng, > > On 31/05/18 12:01, Mark Rutland wrote: >> In do_serror() we already handle nmi_{enter,exit}(), so there's no need >> for that here. > > Even better: nmi_enter() has a BUG_ON(in_nmi()).
There are two places call the arm64_is_fatal_ras_serror(): 1. do_serror() 2. kvm_handle_guest_serror() Yes, the do_serror() already handle nmi_{enter,exit}(), so the arm64_is_fatal_ras_serror() does not need to handle it again. For the kvm_handle_guest_serror(), it does not handle the nmi_{enter,exit}(), so should we add nmi_{enter,exit}() in kvm_handle_guest_serror() before calling arm64_is_fatal_ras_serror()? For the NOTIFY_SEA, I do not know why handle_guest_sea() does not handle the nmi_{enter,exit}(). James, does we miss it in handle_guest_sea()? > > >> TBH, I don't understand why do_sea() does that conditionally today. >> Unless there's some constraint I'm missing, > > APEI uses a different fixmap entry and locks when in_nmi(). This was because > we > may interrupt the irq-masked region in APEI that was using the regular memory. > (e.g. the 'polled' notification, or something backed by an interrupt.) But, > Borislav has spotted other things in here that are broken[0]. I'm working on > rolling all that into 'v5' of the in_nmi() rework stuff. > > We currently get away with this on arm because 'SEA' is the only NMI-like > thing, > and it occurs synchronously. The problem cases are all also cases where the > kernel text is corrupt, which we can't possibly hope to handle. > > For NOTIFY_SDEI and NOTIFY_SEI this is the wrong pattern as these are > asynchronous. do_serror() has already done most of the work for NOTIFY_SEI, > but > we need to use the estatus queue in APEI, which is currently x86 only. I think this patch can based on you 'v5' of the in_nmi() rework stuff > > >> I think it would make more >> sense to do that regardless of whether the interrupted context had >> interrupts enabled. James -- does that make sense to you? >> >> If you update the prior patch with a stub for !CONFIG_ACPI_APEI_SEI, you >> can simplify all of the above additions down to: >> >> if (!ghes_notify_sei()) >> return; >> >> ... which would look a lot nicer. > > The code that calls ghes_notify_sei() may need calling by KVM too, but its > default action to an 'unclaimed' SError will be different. > Because of the race between memory_failure() and return-to-userspace, we may > need to kick the irq work queue (if we can), as we return from do_serror(). > [1] > and [2] provide an example for NOTIFY_SEA. SDEI does this by returning to the > kernel through the IRQ handler, (which handles the KVM case too). I can kick the IRQ work queue as you do for the NOTIFY_SEA and NOTIFY_SDEI. > > > I think this series is unsafe until we can use the estatus queue in APEI. Its > also missing the handling for an SError interrupting a KVM guest. how about this series is based on your patches that uses the estatus queue in APEI to make it safe? when an SError interrupting a KVM guest, it will trap to hypervisor, hypervisor will call below software stack to handle it: kvm_handle_guest_serror()->arm64_is_fatal_ras_serror()->ghes_notify_sei() so it already handles the case that an SError interrupting a KVM guest. > > > Thanks, > > James > > [0] https://www.spinics.net/lists/arm-kernel/msg653332.html > [1] https://www.spinics.net/lists/arm-kernel/msg649237.html > [2] https://www.spinics.net/lists/arm-kernel/msg649239.html > > . >