Re: [PATCH v8 4/5] x86/mm: Add noalias variants of set_memory_*crypted() functions

Sathyanarayanan Kuppuswamy
2022-07-20T14:56:12Z

Hi Kirill,

On 7/19/22 2:55 PM, Kirill A. Shutemov wrote:
> On Tue, Jul 19, 2022 at 10:10:20AM -0700, Sathyanarayanan Kuppuswamy wrote:
>>>> +static struct shmem_priv intel_shmem = {
>>>> + .init = intel_shmem_init,
>>>> + .alloc = intel_shmem_alloc,
>>>> + .free = intel_shmem_free,
>>>> +};
>>>
>>> Hm. What is Intel-specific here. Looks like a generic thing, no?
>>>
>>> Maybe just drop all vendor stuff. CC_ATTR_MEM_ENCRYPT should be enough.
>>
>> I thought that not all CC vendors would want to use DMA APIs for shared
>> buffer allocation. So adding a vendor layer would give them a way to implement
>> their own model.
>
> set_memory_decrypted() is gated by CC_ATTR_MEM_ENCRYPT and it is the only
> requirement for functionality AFAICS.

Makes sense. I think CC_ATTR_GUEST_MEM_ENCRYPT is the better check here. It
force enables the SWIOTLB usage.

diff --git a/arch/x86/coco/Makefile b/arch/x86/coco/Makefile
index c816acf78b6a..96fc4ec4497f 100644
--- a/arch/x86/coco/Makefile
+++ b/arch/x86/coco/Makefile
@@ -3,6 +3,6 @@ CFLAGS_REMOVE_core.o = -pg
KASAN_SANITIZE_core.o := n
CFLAGS_core.o += -fno-stack-protector

-obj-y += core.o
+obj-y += core.o mem.o

obj-$(CONFIG_INTEL_TDX_GUEST) += tdx/
diff --git a/arch/x86/coco/mem.c b/arch/x86/coco/mem.c
new file mode 100644
index 000000000000..ef76a8accc1e
--- /dev/null
+++ b/arch/x86/coco/mem.c
@@ -0,0 +1,82 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Confidential Computing Decrypted Memory Allocator
+ *
+ * Copyright (C) 2022 Intel Corporation, Inc.
+ *
+ */
+
+#undef pr_fmt
+#define pr_fmt(fmt) "cc/mem: " fmt
+
+#include <linux/export.h>
+#include <linux/mm.h>
+#include <linux/cc_platform.h>
+#include <linux/set_memory.h>
+#include <linux/platform_device.h>
+#include <linux/dma-mapping.h>
+
+#include <asm/coco.h>
+#include <asm/processor.h>
+
+#define CC_MEM_DRIVER "ccmem"
+
+struct platform_device *mem_pdev;
+dma_addr_t handle;
+
+/* Allocate decrypted memory of given size */
+void *cc_decrypted_alloc(size_t size, gfp_t gfp)
+{
+ if (!mem_pdev)
+ return NULL;
+
+ return dma_alloc_coherent(&mem_pdev->dev, size, &handle, gfp);
+}
+
+/* Free given decrypted memory */
+void cc_decrypted_free(void *addr, size_t size)
+{
+ if (!mem_pdev)
+ return;
+
+ dma_free_coherent(&mem_pdev->dev, size, addr, handle);
+}
+
+static int cc_mem_probe(struct platform_device *pdev)
+{
+ if (dma_set_coherent_mask(&pdev->dev, DMA_BIT_MASK(64)))
+ return -EIO;
+
+ mem_pdev = pdev;
+
+ return 0;
+}
+
+static struct platform_driver cc_mem_driver = {
+ .probe = cc_mem_probe,
+ .driver = {
+ .name = CC_MEM_DRIVER,
+ },
+};
+
+static int __init cc_mem_init(void)
+{
+ struct platform_device *pdev;
+ int ret;
+
+ if (!cc_platform_has(CC_ATTR_GUEST_MEM_ENCRYPT))
+ return -ENODEV;
+
+ ret = platform_driver_register(&cc_mem_driver);
+ if (ret)
+ return ret;
+
+ pdev = platform_device_register_simple(CC_MEM_DRIVER, -1, NULL, 0);
+ if (IS_ERR(pdev)) {
+ platform_driver_unregister(&cc_mem_driver);
+ return PTR_ERR(pdev);
+ }
+
+ return 0;
+}
+device_initcall(cc_mem_init);
diff --git a/arch/x86/include/asm/coco.h b/arch/x86/include/asm/coco.h
index 3d98c3a60d34..9d616d9e3405 100644
--- a/arch/x86/include/asm/coco.h
+++ b/arch/x86/include/asm/coco.h
@@ -17,6 +17,8 @@ void cc_set_mask(u64 mask);
#ifdef CONFIG_ARCH_HAS_CC_PLATFORM
u64 cc_mkenc(u64 val);
u64 cc_mkdec(u64 val);
+void *cc_decrypted_alloc(size_t size, gfp_t gfp);
+void cc_decrypted_free(void *addr, size_t size);
#else
static inline u64 cc_mkenc(u64 val)
{
@@ -27,6 +29,10 @@ static inline u64 cc_mkdec(u64 val)
{
return val;
}
+
+void *cc_decrypted_alloc(size_t size, gfp_t gfp) { return NULL; }
+void cc_decrypted_free(void *addr, size_t size) { }
+
#endif

#endif /* _ASM_X86_COCO_H

>

--
Sathyanarayanan Kuppuswamy
Linux Kernel Developer