linux-kernel - Re: [PATCH] KVM: PPC: Book3S HV: Always flush TLB in kvmppc_alloc_reset

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Message-ID: <20180111095451.GG24294@fergus.ozlabs.ibm.com>
Date:   Thu, 11 Jan 2018 20:54:51 +1100
From:   Paul Mackerras <paulus@...abs.org>
To:     David Gibson <david@...son.dropbear.id.au>
Cc:     surajjs@....ibm.com, spopovyc@...hat.com, kvm@...r.kernel.org,
        kvm-ppc@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] KVM: PPC: Book3S HV: Always flush TLB in
 kvmppc_alloc_reset_hpt()

On Wed, Jan 10, 2018 at 05:04:39PM +1100, David Gibson wrote:
> The KVM_PPC_ALLOCATE_HTAB ioctl(), implemented by kvmppc_alloc_reset_hpt()
> is supposed to completely clear and reset a guest's Hashed Page Table (HPT)
> allocating or re-allocating it if necessary.
> 
> In the case where an HPT of the right size already exists and it just
> zeroes it, it forces a TLB flush on all guest CPUs, to remove any stale TLB
> entries loaded from the old HPT.
> 
> However, that situation can arise when the HPT is resizing as well - or
> even when switching from an RPT to HPT - so those cases need a TLB flush as
> well.
> 
> So, move the TLB flush to trigger in all cases except for errors.
> 
> Signed-off-by: David Gibson <david@...son.dropbear.id.au>
> ---
>  arch/powerpc/kvm/book3s_64_mmu_hv.c | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
> 
> Paul, this is based on Paolo's KVM tree, but it should apply without
> modification to pretty much any vaguely current tree.  It's a pretty
> nasty bug - the case we've found hitting it in the wild is a bit
> esoteric, but it could in theory affect other situations as well.
> 
> Please apply ASAP, and should probably be queued for the stable
> branches as well.

Thanks, applied to my kvm-ppc-fixes branch, and I added
cc: stable@...r.kernel.org.

Paul.