linux-kernel - RE: [PATCH v2 1/1] KVM: arm64: allow the VM to select DEVICE_* and NORMAL

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Message-ID: <296657c5b09f46a1ac6e4d993fbc0875@huawei.com>
Date:   Tue, 5 Dec 2023 14:16:51 +0000
From:   Shameerali Kolothum Thodi <shameerali.kolothum.thodi@...wei.com>
To:     Catalin Marinas <catalin.marinas@....com>,
        Marc Zyngier <maz@...nel.org>
CC:     "ankita@...dia.com" <ankita@...dia.com>,
        "jgg@...dia.com" <jgg@...dia.com>,
        "oliver.upton@...ux.dev" <oliver.upton@...ux.dev>,
        "suzuki.poulose@....com" <suzuki.poulose@....com>,
        yuzenghui <yuzenghui@...wei.com>,
        "will@...nel.org" <will@...nel.org>,
        "ardb@...nel.org" <ardb@...nel.org>,
        "akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
        "gshan@...hat.com" <gshan@...hat.com>,
        "aniketa@...dia.com" <aniketa@...dia.com>,
        "cjia@...dia.com" <cjia@...dia.com>,
        "kwankhede@...dia.com" <kwankhede@...dia.com>,
        "targupta@...dia.com" <targupta@...dia.com>,
        "vsethi@...dia.com" <vsethi@...dia.com>,
        "acurrid@...dia.com" <acurrid@...dia.com>,
        "apopple@...dia.com" <apopple@...dia.com>,
        "jhubbard@...dia.com" <jhubbard@...dia.com>,
        "danw@...dia.com" <danw@...dia.com>,
        "mochs@...dia.com" <mochs@...dia.com>,
        "kvmarm@...ts.linux.dev" <kvmarm@...ts.linux.dev>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "lpieralisi@...nel.org" <lpieralisi@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linyufeng (A)" <linyufeng3@...wei.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@....com>
> Sent: Tuesday, December 5, 2023 11:41 AM
> To: Marc Zyngier <maz@...nel.org>
> Cc: ankita@...dia.com; Shameerali Kolothum Thodi
> <shameerali.kolothum.thodi@...wei.com>; jgg@...dia.com;
> oliver.upton@...ux.dev; suzuki.poulose@....com; yuzenghui
> <yuzenghui@...wei.com>; will@...nel.org; ardb@...nel.org; akpm@...ux-
> foundation.org; gshan@...hat.com; aniketa@...dia.com; cjia@...dia.com;
> kwankhede@...dia.com; targupta@...dia.com; vsethi@...dia.com;
> acurrid@...dia.com; apopple@...dia.com; jhubbard@...dia.com;
> danw@...dia.com; mochs@...dia.com; kvmarm@...ts.linux.dev;
> kvm@...r.kernel.org; lpieralisi@...nel.org; linux-kernel@...r.kernel.org;
> linux-arm-kernel@...ts.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@...dia.com> wrote:
> > > From: Ankit Agrawal <ankita@...dia.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,
Shameer