Re: [PATCH v5 01/16] x86/mm: Move force_dma_unencrypted() to common code

Tom Lendacky
2021-10-20T16:11:26Z

On 10/8/21 7:36 PM, Kuppuswamy Sathyanarayanan wrote:
> From: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
>
> Intel TDX doesn't allow VMM to access guest private memory. Any memory
> that is required for communication with VMM must be shared explicitly
> by setting the bit in page table entry. After setting the shared bit,
> the conversion must be completed with MapGPA hypercall. Details about
> MapGPA hypercall can be found in [1], sec 3.2.
>
> The call informs VMM about the conversion between private/shared
> mappings. The shared memory is similar to unencrypted memory in AMD
> SME/SEV terminology but the underlying process of sharing/un-sharing
> the memory is different for Intel TDX guest platform.
>
> SEV assumes that I/O devices can only do DMA to "decrypted" physical
> addresses without the C-bit set. In order for the CPU to interact with
> this memory, the CPU needs a decrypted mapping. To add this support,
> AMD SME code forces force_dma_unencrypted() to return true for
> platforms that support AMD SEV feature. It will be used for DMA memory
> allocation API to trigger set_memory_decrypted() for platforms that
> support AMD SEV feature.
>
> TDX is similar. So, to communicate with I/O devices, related pages need
> to be marked as shared. As mentioned above, shared memory in TDX
> architecture is similar to decrypted memory in AMD SME/SEV. So similar
> to AMD SEV, force_dma_unencrypted() has to forced to return true. This
> support is added in other patches in this series.
>
> So move force_dma_unencrypted() out of AMD specific code and call AMD
> specific (amd_force_dma_unencrypted()) initialization function from it.
> force_dma_unencrypted() will be modified by later patches to include
> Intel TDX guest platform specific initialization.
>
> Also, introduce new config option X86_MEM_ENCRYPT_COMMON that has to be
> selected by all x86 memory encryption features. This will be selected
> by both AMD SEV and Intel TDX guest config options.
>
> This is preparation for TDX changes in DMA code and it has no
> functional change.

Can force_dma_unencrypted() be moved to arch/x86/kernel/cc_platform.c,
instead of creating a new file? It might fit better with patch #6.

Thanks,
Tom

>
> [1] - https://software.intel.com/content/dam/develop/external/us/en/documents/intel-tdx-guest-hypervisor-communication-interface.pdf
>
> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
> Reviewed-by: Andi Kleen <ak@linux.intel.com>
> Reviewed-by: Tony Luck <tony.luck@intel.com>
> Signed-off-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.intel.com>
> ---
>
> Changes since v4:
> * Removed used we/you from commit log.
>
> Change since v3:
> * None
>
> Changes since v1:
> * Removed sev_active(), sme_active() checks in force_dma_unencrypted().
>
> arch/x86/Kconfig | 8 ++++++--
> arch/x86/include/asm/mem_encrypt_common.h | 18 ++++++++++++++++++
> arch/x86/mm/Makefile | 2 ++
> arch/x86/mm/mem_encrypt.c | 3 ++-
> arch/x86/mm/mem_encrypt_common.c | 17 +++++++++++++++++
> 5 files changed, 45 insertions(+), 3 deletions(-)
> create mode 100644 arch/x86/include/asm/mem_encrypt_common.h
> create mode 100644 arch/x86/mm/mem_encrypt_common.c
>
> diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
> index af49ad084919..37b27412f52e 100644
> --- a/arch/x86/Kconfig
> +++ b/arch/x86/Kconfig
> @@ -1519,16 +1519,20 @@ config X86_CPA_STATISTICS
> helps to determine the effectiveness of preserving large and huge
> page mappings when mapping protections are changed.
>
> +config X86_MEM_ENCRYPT_COMMON
> + select ARCH_HAS_FORCE_DMA_UNENCRYPTED
> + select DYNAMIC_PHYSICAL_MASK
> + def_bool n
> +
> config AMD_MEM_ENCRYPT
> bool "AMD Secure Memory Encryption (SME) support"
> depends on X86_64 && CPU_SUP_AMD
> select DMA_COHERENT_POOL
> - select DYNAMIC_PHYSICAL_MASK
> select ARCH_USE_MEMREMAP_PROT
> - select ARCH_HAS_FORCE_DMA_UNENCRYPTED
> select INSTRUCTION_DECODER
> select ARCH_HAS_RESTRICTED_VIRTIO_MEMORY_ACCESS
> select ARCH_HAS_CC_PLATFORM
> + select X86_MEM_ENCRYPT_COMMON
> help
> Say yes to enable support for the encryption of system memory.
> This requires an AMD processor that supports Secure Memory
> diff --git a/arch/x86/include/asm/mem_encrypt_common.h b/arch/x86/include/asm/mem_encrypt_common.h
> new file mode 100644
> index 000000000000..697bc40a4e3d
> --- /dev/null
> +++ b/arch/x86/include/asm/mem_encrypt_common.h
> @@ -0,0 +1,18 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +/* Copyright (C) 2020 Intel Corporation */
> +#ifndef _ASM_X86_MEM_ENCRYPT_COMMON_H
> +#define _ASM_X86_MEM_ENCRYPT_COMMON_H
> +
> +#include <linux/mem_encrypt.h>
> +#include <linux/device.h>
> +
> +#ifdef CONFIG_AMD_MEM_ENCRYPT
> +bool amd_force_dma_unencrypted(struct device *dev);
> +#else /* CONFIG_AMD_MEM_ENCRYPT */
> +static inline bool amd_force_dma_unencrypted(struct device *dev)
> +{
> + return false;
> +}
> +#endif /* CONFIG_AMD_MEM_ENCRYPT */
> +
> +#endif
> diff --git a/arch/x86/mm/Makefile b/arch/x86/mm/Makefile
> index 5864219221ca..b31cb52bf1bd 100644
> --- a/arch/x86/mm/Makefile
> +++ b/arch/x86/mm/Makefile
> @@ -52,6 +52,8 @@ obj-$(CONFIG_X86_INTEL_MEMORY_PROTECTION_KEYS) += pkeys.o
> obj-$(CONFIG_RANDOMIZE_MEMORY) += kaslr.o
> obj-$(CONFIG_PAGE_TABLE_ISOLATION) += pti.o
>
> +obj-$(CONFIG_X86_MEM_ENCRYPT_COMMON) += mem_encrypt_common.o
> +
> obj-$(CONFIG_AMD_MEM_ENCRYPT) += mem_encrypt.o
> obj-$(CONFIG_AMD_MEM_ENCRYPT) += mem_encrypt_identity.o
> obj-$(CONFIG_AMD_MEM_ENCRYPT) += mem_encrypt_boot.o
> diff --git a/arch/x86/mm/mem_encrypt.c b/arch/x86/mm/mem_encrypt.c
> index 23d54b810f08..5d7fbed73949 100644
> --- a/arch/x86/mm/mem_encrypt.c
> +++ b/arch/x86/mm/mem_encrypt.c
> @@ -31,6 +31,7 @@
> #include <asm/processor-flags.h>
> #include <asm/msr.h>
> #include <asm/cmdline.h>
> +#include <asm/mem_encrypt_common.h>
>
> #include "mm_internal.h"
>
> @@ -362,7 +363,7 @@ int __init early_set_memory_encrypted(unsigned long vaddr, unsigned long size)
> }
>
> /* Override for DMA direct allocation check - ARCH_HAS_FORCE_DMA_UNENCRYPTED */
> -bool force_dma_unencrypted(struct device *dev)
> +bool amd_force_dma_unencrypted(struct device *dev)
> {
> /*
> * For SEV, all DMA must be to unencrypted addresses.
> diff --git a/arch/x86/mm/mem_encrypt_common.c b/arch/x86/mm/mem_encrypt_common.c
> new file mode 100644
> index 000000000000..f063c885b0a5
> --- /dev/null
> +++ b/arch/x86/mm/mem_encrypt_common.c
> @@ -0,0 +1,17 @@
> +// SPDX-License-Identifier: GPL-2.0-only
> +/*
> + * Memory Encryption Support Common Code
> + *
> + * Copyright (C) 2021 Intel Corporation
> + *
> + * Author: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.intel.com>
> + */
> +
> +#include <asm/mem_encrypt_common.h>
> +#include <linux/dma-mapping.h>
> +
> +/* Override for DMA direct allocation check - ARCH_HAS_FORCE_DMA_UNENCRYPTED */
> +bool force_dma_unencrypted(struct device *dev)
> +{
> + return amd_force_dma_unencrypted(dev);
> +}
>