linux-kernel - Re: [PATCH] device-dax: map dax memory as decrypted in CoCo guests

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Message-ID: <0bae453d-b4a8-3132-9fd0-bca0eece6a74@amd.com>
Date: Fri, 23 Aug 2024 14:09:10 +0200
From: "Gupta, Pankaj" <pankaj.gupta@....com>
To: Kevin Loughlin <kevinloughlin@...gle.com>,
 Dan Williams <dan.j.williams@...el.com>,
 Vishal Verma <vishal.l.verma@...el.com>, Dave Jiang <dave.jiang@...el.com>,
 nvdimm@...ts.linux.dev, linux-cxl@...r.kernel.org,
 linux-kernel@...r.kernel.org
Cc: changyuanl@...gle.com, pgonda@...gle.com, sidtelang@...gle.com,
 tytso@....edu, pasha.tatashin@...een.com, thomas.lendacky@....com
Subject: Re: [PATCH] device-dax: map dax memory as decrypted in CoCo guests

> Confidential Computing (CoCo) guests encrypt private memory by default.
> DAX memory regions allow a guest to bypass its own (private) page cache
> and instead use host memory, which is not private to the guest.
> 
> Commit 867400af90f1 ("mm/memremap.c: map FS_DAX device memory as
> decrypted") only ensures that FS_DAX memory is appropriately marked as
> decrypted. As such, also mark device-dax memory as decrypted.

Overall patch seems OK to me.

How can I test this? Can I test it with virtio-pmem device?

Thanks,
Pankaj
> 
> Signed-off-by: Kevin Loughlin <kevinloughlin@...gle.co > ---
>   drivers/dax/device.c | 3 +++
>   1 file changed, 3 insertions(+)
> 
> diff --git a/drivers/dax/device.c b/drivers/dax/device.c
> index 2051e4f73c8a..a284442d7ecc 100644
> --- a/drivers/dax/device.c
> +++ b/drivers/dax/device.c
> @@ -11,6 +11,7 @@
>   #include <linux/fs.h>
>   #include <linux/mm.h>
>   #include <linux/mman.h>
> +#include <linux/cc_platform.h>
>   #include "dax-private.h"
>   #include "bus.h"
>   
> @@ -303,6 +304,8 @@ static int dax_mmap(struct file *filp, struct vm_area_struct *vma)
>   
>   	vma->vm_ops = &dax_vm_ops;
>   	vm_flags_set(vma, VM_HUGEPAGE);
> +	if (cc_platform_has(CC_ATTR_MEM_ENCRYPT))
> +		vma->vm_page_prot = pgprot_decrypted(vma->vm_page_prot);
>   	return 0;
>   }
>