linux-kernel - Re: [PATCH v8 4/5] x86/mm: Add noalias variants of set_memory

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Date:   Wed, 20 Jul 2022 07:56:04 -0700
From:   Sathyanarayanan Kuppuswamy 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>
To:     "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
Cc:     "Kirill A. Shutemov" <kirill@...temov.name>,
        Kai Huang <kai.huang@...el.com>,
        Dave Hansen <dave.hansen@...el.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
        "H . Peter Anvin" <hpa@...or.com>, Tony Luck <tony.luck@...el.com>,
        Andi Kleen <ak@...ux.intel.com>,
        Wander Lairson Costa <wander@...hat.com>,
        Isaku Yamahata <isaku.yamahata@...il.com>,
        marcelo.cerri@...onical.com, tim.gardner@...onical.com,
        khalid.elmously@...onical.com, philip.cox@...onical.com,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v8 4/5] x86/mm: Add noalias variants of
 set_memory_*crypted() functions

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