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Date: Thu, 8 Feb 2024 13:03:27 +0000
From: Catalin Marinas <catalin.marinas@arm.com>
To: ankita@nvidia.com
Cc: jgg@nvidia.com, maz@kernel.org, oliver.upton@linux.dev,
	james.morse@arm.com, suzuki.poulose@arm.com, yuzenghui@huawei.com,
	reinette.chatre@intel.com, surenb@google.com, stefanha@redhat.com,
	brauner@kernel.org, will@kernel.org, mark.rutland@arm.com,
	alex.williamson@redhat.com, kevin.tian@intel.com,
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	David Hildenbrand <david@redhat.com>
Subject: Re: [PATCH v6 2/4] mm: introduce new flag to indicate wc safe
Message-ID: <ZcTRH1rzfPbuQ_qj@arm.com>
References: <20240207204652.22954-1-ankita@nvidia.com>
 <20240207204652.22954-3-ankita@nvidia.com>
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In-Reply-To: <20240207204652.22954-3-ankita@nvidia.com>

On Thu, Feb 08, 2024 at 02:16:50AM +0530, ankita@nvidia.com wrote:
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index f5a97dec5169..884c068a79eb 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -391,6 +391,20 @@ extern unsigned int kobjsize(const void *objp);
>  # define VM_UFFD_MINOR		VM_NONE
>  #endif /* CONFIG_HAVE_ARCH_USERFAULTFD_MINOR */
>  
> +/*
> + * This flag is used to connect VFIO to arch specific KVM code. It
> + * indicates that the memory under this VMA is safe for use with any
> + * non-cachable memory type inside KVM. Some VFIO devices, on some
> + * platforms, are thought to be unsafe and can cause machine crashes if
> + * KVM does not lock down the memory type.
> + */
> +#ifdef CONFIG_64BIT
> +#define VM_VFIO_ALLOW_WC_BIT	39
> +#define VM_VFIO_ALLOW_WC	BIT(VM_VFIO_ALLOW_WC_BIT)
> +#else
> +#define VM_VFIO_ALLOW_WC	VM_NONE
> +#endif

Adding David Hildenbrand to this thread as well since we briefly
discussed potential alternatives (not sure we came to any conclusion).

-- 
Catalin