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

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Message-ID: <20240814205303.2619373-1-kevinloughlin@google.com>
Date: Wed, 14 Aug 2024 20:53:03 +0000
From: Kevin Loughlin <kevinloughlin@...gle.com>
To: 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: kevinloughlin@...gle.com, changyuanl@...gle.com, pgonda@...gle.com, 
	sidtelang@...gle.com, tytso@....edu, pasha.tatashin@...een.com, 
	thomas.lendacky@....com, pankaj.gupta@....com
Subject: [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.

Signed-off-by: Kevin Loughlin <kevinloughlin@...gle.com>
---
 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;
 }
 
-- 
2.46.0.76.ge559c4bf1a-goog