Re: [Qemu-devel] [PATCH 0/4] target-ppc/spapr: Add FWNMI support in QEMU for PowerKVM guests

[David Gibson <david@gibson.dropbear.id.au>]

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On Wed, Nov 11, 2015 at 10:45:00PM +0530, Aravinda Prasad wrote:
> This series of patches add support for FWNMI in PowerKVM guests.
> 
> Memory error such as bit flips that cannot be corrected
> by hardware is passed on to the kernel for handling
> by raising machine check exception (an NMI). Upon such
> machine check exception, if the address in error belongs
> to guest then KVM causes a guest exit with KVM_EXIT_NMI
> exit reason [1].
> 
> This patch series adds functionality to pass on such
> machine check exception to the guest kernel by suitably
> handling KVM_EXIT_NMI exit and building the error log.
> This patch series explores the alternate design
> discussed in the QEMU mailing list [2], [3].
> 
> In earlier design [2] KVM invoked guest's NMI interrupt
> vector 0x200 upon machine check exception, while QEMU
> patched 0x200 vector to issue hcall to facilitate
> building and copying of error log into RTAS space.
> 
> The new design simplifies couple of things. Thanks to
> David Gibson for the suggestion:
> 
>     - Eliminates patching of 0x200 interrupt vector from
>       QEMU, hence, trampoline not required
>     - Avoids introducing a new private hcall to be called
>       from guest's 0x200 vector to enable QEMU to build
>       error log
>     - Simplifies re-trying by other processors when one
>       of the processor is consuming/processing the error
>       log.
> 
> [1] http://marc.info/?l=kvm-ppc&m=144726114408289
> [2] https://lists.nongnu.org/archive/html/qemu-devel/2014-11/msg00813.html
> [3]
> https://lists.nongnu.org/archive/html/qemu-devel/2015-08/msg00898.html

This looks basically good, although I have some concerns noted in
replies to patches 3 & 4.  We can't merge this, though, until the
prerequisite kernel and SLOF patches are merged, so this won't make it
into 2.5 (hard freeze today).

-- 
David Gibson			| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you.  NOT _the_ _other_
				| _way_ _around_!
http://www.ozlabs.org/~dgibson

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