RE: [PATCH v2 1/1] KVM: arm64: allow the VM to select DEVICE_* and NORMAL_NC for IO memory

[Shameerali Kolothum Thodi <shameerali.kolothum.thodi@huawei.com>]

> -----Original Message-----
> From: Shameerali Kolothum Thodi
> Sent: Tuesday, December 5, 2023 2:17 PM
> To: 'Catalin Marinas' <catalin.marinas@arm.com>; Marc Zyngier
> <maz@kernel.org>
> Cc: ankita@nvidia.com; jgg@nvidia.com; oliver.upton@linux.dev;
> suzuki.poulose@arm.com; yuzenghui <yuzenghui@huawei.com>;
> will@kernel.org; ardb@kernel.org; akpm@linux-foundation.org;
> gshan@redhat.com; aniketa@nvidia.com; cjia@nvidia.com;
> kwankhede@nvidia.com; targupta@nvidia.com; vsethi@nvidia.com;
> acurrid@nvidia.com; apopple@nvidia.com; jhubbard@nvidia.com;
> danw@nvidia.com; mochs@nvidia.com; kvmarm@lists.linux.dev;
> kvm@vger.kernel.org; lpieralisi@kernel.org; linux-kernel@vger.kernel.org;
> linux-arm-kernel@lists.infradead.org; linyufeng (A)
> <linyufeng3@huawei.com>
> Subject: RE: [PATCH v2 1/1] KVM: arm64: allow the VM to select DEVICE_*
> and NORMAL_NC for IO memory
> 
> 
> 
> > -----Original Message-----
> > From: Catalin Marinas <catalin.marinas@arm.com>
> > Sent: Tuesday, December 5, 2023 11:41 AM
> > To: Marc Zyngier <maz@kernel.org>
> > Cc: ankita@nvidia.com; Shameerali Kolothum Thodi
> > <shameerali.kolothum.thodi@huawei.com>; jgg@nvidia.com;
> > oliver.upton@linux.dev; suzuki.poulose@arm.com; yuzenghui
> > <yuzenghui@huawei.com>; will@kernel.org; ardb@kernel.org;
> akpm@linux-
> > foundation.org; gshan@redhat.com; aniketa@nvidia.com;
> cjia@nvidia.com;
> > kwankhede@nvidia.com; targupta@nvidia.com; vsethi@nvidia.com;
> > acurrid@nvidia.com; apopple@nvidia.com; jhubbard@nvidia.com;
> > danw@nvidia.com; mochs@nvidia.com; kvmarm@lists.linux.dev;
> > kvm@vger.kernel.org; lpieralisi@kernel.org; linux-kernel@vger.kernel.org;
> > linux-arm-kernel@lists.infradead.org
> > Subject: Re: [PATCH v2 1/1] KVM: arm64: allow the VM to select DEVICE_*
> > and NORMAL_NC for IO memory
> >
> > + Lorenzo, he really needs to be on this thread.
> >
> > On Tue, Dec 05, 2023 at 09:21:28AM +0000, Marc Zyngier wrote:
> > > On Tue, 05 Dec 2023 03:30:15 +0000,
> > > <ankita@nvidia.com> wrote:
> > > > From: Ankit Agrawal <ankita@nvidia.com>
> > > >
> > > > Currently, KVM for ARM64 maps at stage 2 memory that is considered
> > device
> > > > (i.e. it is not RAM) with DEVICE_nGnRE memory attributes; this setting
> > > > overrides (as per the ARM architecture [1]) any device MMIO mapping
> > > > present at stage 1, resulting in a set-up whereby a guest operating
> > > > system cannot determine device MMIO mapping memory attributes on
> > its
> > > > own but it is always overridden by the KVM stage 2 default.
> > [...]
> > > Despite the considerable increase in the commit message length, a
> > > number of questions are left unanswered:
> > >
> > > - Shameer reported a regression on non-FWB systems, breaking device
> > >   assignment:
> > >
> > >
> >
> https://lore.kernel.org/all/af13ed63dc9a4f26a6c958ebfa77d78a@huawei.co
> > m/
> >
> > This referred to the first patch in the old series which was trying to
> > make the Stage 2 cacheable based on the vma attributes. That patch has
> > been dropped for now. It would be good if Shameer confirms this was the
> > problem.
> >
> 
> Yes, that was related to the first patch. We will soon test this on both FWB
> and
> non-FWB platforms and report back.
> 

Thanks to Yufeng, the test on both FWB and non-FWB platforms with a  GPU dev
assignment looks fine with this patch.

Shameer