[stable PATCH 1/2] arm64: Fix mismatched cache line size detection

Greg KH greg at kroah.com
Thu Sep 13 05:19:51 PDT 2018

On Thu, Sep 13, 2018 at 10:54:06AM +0100, Suzuki K Poulose wrote:
> Hi Greg,
> On 12/09/18 20:38, Greg KH wrote:
> > On Tue, Sep 04, 2018 at 10:10:09AM +0100, Suzuki K Poulose wrote:
> > > commit 4c4a39dd5fe2d13e2d2fa5fceb8ef95d19fc389a upstream
> > > 
> > > If there is a mismatch in the I/D min line size, we must
> > > always use the system wide safe value both in applications
> > > and in the kernel, while performing cache operations. However,
> > > we have been checking more bits than just the min line sizes,
> > > which triggers false negatives. We may need to trap the user
> > > accesses in such cases, but not necessarily patch the kernel.
> > > 
> > > This patch fixes the check to do the right thing as advertised.
> > > A new capability will be added to check mismatches in other
> > > fields and ensure we trap the CTR accesses.
> > > 
> > > Fixes: be68a8aaf925 ("arm64: cpufeature: Fix CTR_EL0 field definitions")
> > > Cc: <stable at vger.kernel.org> # v4.9
> > 
> > Why 4.9?  be68a8aaf925 only showed up in 4.16 and was backported only to
> > 4.14-stable.  Not to 4.9-stable from what I can tell.
> Now when you asked this, I realise that the Fixes tags were not sufficient.
> Actually this series fixes a bit more than the commit: be68a8aaf925 ("arm64: cpufeature:
> Fix CTR_EL0 field definitions"). I think these patches should have :
> Fixes: commit 116c81f427ff6c5 ("arm64: Work around systems with mismatched cache line sizes")
> and
> Enable trapping on mismatched bits in CTR for IDC/DIC, which were
> added to v8.3 onwards.
> Essentially these patches makes sure that we trap accesses to
> CTR_EL0 when some of the fields are mismatched across CPUs, so
> that the CPUs get a consistent view of the cache properties
> throughout the system. It also makes sure that we put out
> correct information about why we trap accesses to the CTR_EL0
> accesses from the userspace.
> Hope this helps. The same applies for the next patch.

Yes, it does help.  But these patches do not apply to the 4.14.y series,
which I also need to apply them to (you don't want to move from 4.9.y to
4.14.y and get a regression.)

So can you provide backports for both of these patches for 4.14.y?  Then
I would be glad to queue these all up.


greg k-h

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