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

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Message-ID: <BY5PR12MB37634D7D2B66D772986C4C1DB08BA@BY5PR12MB3763.namprd12.prod.outlook.com>
Date:   Thu, 7 Dec 2023 02:53:23 +0000
From:   Ankit Agrawal <ankita@...dia.com>
To:     Catalin Marinas <catalin.marinas@....com>,
        Jason Gunthorpe <jgg@...dia.com>
CC:     Marc Zyngier <maz@...nel.org>,
        Shameerali Kolothum Thodi 
        <shameerali.kolothum.thodi@...wei.com>,
        "oliver.upton@...ux.dev" <oliver.upton@...ux.dev>,
        "suzuki.poulose@....com" <suzuki.poulose@....com>,
        "yuzenghui@...wei.com" <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>,
        Aniket Agashe <aniketa@...dia.com>, Neo Jia <cjia@...dia.com>,
        Kirti Wankhede <kwankhede@...dia.com>,
        "Tarun Gupta (SW-GPU)" <targupta@...dia.com>,
        Vikram Sethi <vsethi@...dia.com>,
        Andy Currid <acurrid@...dia.com>,
        Alistair Popple <apopple@...dia.com>,
        John Hubbard <jhubbard@...dia.com>,
        Dan Williams <danw@...dia.com>, Matt Ochs <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>
Subject: Re: [PATCH v2 1/1] KVM: arm64: allow the VM to select DEVICE_* and
 NORMAL_NC for IO memory



>On Wed, Dec 06, 2023 at 03:03:56PM -0400, Jason Gunthorpe wrote:
>> On Wed, Dec 06, 2023 at 06:58:44PM +0000, Catalin Marinas wrote:
>> > -------------8<----------------------------
>> > diff --git a/drivers/vfio/pci/vfio_pci_core.c b/drivers/vfio/pci/vfio_pci_core.c
>> > index 1929103ee59a..b89d2dfcd534 100644
>> > --- a/drivers/vfio/pci/vfio_pci_core.c
>> > +++ b/drivers/vfio/pci/vfio_pci_core.c
>> > @@ -1863,7 +1863,7 @@ int vfio_pci_core_mmap(struct vfio_device *core_vdev, struct vm_area_struct *vma
>> >      * See remap_pfn_range(), called from vfio_pci_fault() but we can't
>> >      * change vm_flags within the fault handler.  Set them now.
>> >      */
>> > -   vm_flags_set(vma, VM_IO | VM_PFNMAP | VM_DONTEXPAND | VM_DONTDUMP);
>> > +   vm_flags_set(vma, VM_VFIO | VM_IO | VM_PFNMAP | VM_DONTEXPAND | VM_DONTDUMP);
>> >     vma->vm_ops = &vfio_pci_mmap_ops;
>> >
>> >     return 0;
>> > diff --git a/include/linux/mm.h b/include/linux/mm.h
>> > index 418d26608ece..6df46fd7836a 100644
>> > --- a/include/linux/mm.h
>> > +++ b/include/linux/mm.h
>> > @@ -391,6 +391,13 @@ extern unsigned int kobjsize(const void *objp);
>> >  # define VM_UFFD_MINOR             VM_NONE
>> >  #endif /* CONFIG_HAVE_ARCH_USERFAULTFD_MINOR */
>> >
>> > +#ifdef CONFIG_64BIT
>> > +#define VM_VFIO_BIT                39
>> > +#define VM_VFIO                    BIT(VM_VFIO_BIT)
>> > +#else
>> > +#define VM_VFIO                    VM_NONE
>> > +#endif
>> > +
>> >  /* Bits set in the VMA until the stack is in its final location */
>> >  #define VM_STACK_INCOMPLETE_SETUP (VM_RAND_READ | VM_SEQ_READ | VM_STACK_EARLY)
>> > -------------8<----------------------------
>> >
>> > In KVM, Akita's patch would take this into account, not just rely on
>> > "device==true".
>>
>> Yes, Ankit let's try this please. I would not call it VM_VFIO though
>>
>> VM_VFIO_ALLOW_WC ?
>
> Yeah. I don't really care about the name.

Thanks, I will make the change to set the VM_VFIO_ALLOW_WC flag in vfio.
Then make use of "device==true" and presence of the flag to decide on
setting the S2 as NORMAL_NC.