# Re: \[PATCH v5 07/16\] x86/kvm: Use bounce buffers for TD guest

- From: Tom Lendacky \<thomas.lendacky@amd.com\>
- Date: 2021-10-20 16:39:13 
- List: linux-doc
- Page: https://ratatoskr.run/linux-doc/2021/10/1548555
- Thread: https://ratatoskr.run/linux-pci/2021/10/1535998/t.md

```text
On 10/8/21 7:37 PM, Kuppuswamy Sathyanarayanan wrote:
> From: "Kirill A. Shutemov" <redacted>
>
> Intel TDX doesn't allow VMM to directly access guest private memory.
> Any memory that is required for communication with VMM must be shared
> explicitly. The same rule applies for any DMA to and from TDX guest.
> All DMA pages had to marked as shared pages. A generic way to achieve
> this without any changes to device drivers is to use the SWIOTLB
> framework.
>
> This method of handling is similar to AMD SEV. So extend this support
> for TDX guest as well. Also since there are some common code between
> AMD SEV and TDX guest in mem_encrypt_init(), move it to
> mem_encrypt_common.c and call AMD specific init function from it
>
> Signed-off-by: Kirill A. Shutemov <redacted>
> Reviewed-by: Andi Kleen <redacted>
> Reviewed-by: Tony Luck <tony.luck@intel.com>
> Signed-off-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.intel.com>
> ---
>
> Changes since v4:
>   * Replaced prot_guest_has() with cc_guest_has().
>
> Changes since v3:
>   * Rebased on top of Tom Lendacky's protected guest
>     changes (https://lore.kernel.org/patchwork/cover/1468760/)
>
> Changes since v1:
>   * Removed sme_me_mask check for amd_mem_encrypt_init() in mem_encrypt_init().
>
>   arch/x86/include/asm/mem_encrypt_common.h |  3 +++
>   arch/x86/kernel/tdx.c                     |  2 ++
>   arch/x86/mm/mem_encrypt.c                 |  5 +----
>   arch/x86/mm/mem_encrypt_common.c          | 14 ++++++++++++++
>   4 files changed, 20 insertions(+), 4 deletions(-)
>
> diff --git a/arch/x86/include/asm/mem_encrypt_common.h b/arch/x86/include/asm/mem_encrypt_common.h
> index 697bc40a4e3d..bc90e565bce4 100644
> --- a/arch/x86/include/asm/mem_encrypt_common.h
> +++ b/arch/x86/include/asm/mem_encrypt_common.h
> @@ -8,11 +8,14 @@
>   
>   #ifdef CONFIG_AMD_MEM_ENCRYPT
>   bool amd_force_dma_unencrypted(struct device *dev);
> +void __init amd_mem_encrypt_init(void);
>   #else /* CONFIG_AMD_MEM_ENCRYPT */
>   static inline bool amd_force_dma_unencrypted(struct device *dev)
>   {
>   	return false;
>   }
> +
> +static inline void amd_mem_encrypt_init(void) {}
>   #endif /* CONFIG_AMD_MEM_ENCRYPT */
>   
>   #endif
> diff --git a/arch/x86/kernel/tdx.c b/arch/x86/kernel/tdx.c
> index 433f366ca25c..ce8e3019b812 100644
> --- a/arch/x86/kernel/tdx.c
> +++ b/arch/x86/kernel/tdx.c
> @@ -12,6 +12,7 @@
>   #include <asm/insn.h>
>   #include <asm/insn-eval.h>
>   #include <linux/sched/signal.h> /* force_sig_fault() */
> +#include <linux/swiotlb.h>
>   
>   /* TDX Module call Leaf IDs */
>   #define TDX_GET_INFO			1
> @@ -577,6 +578,7 @@ void __init tdx_early_init(void)
>   	pv_ops.irq.halt = tdx_halt;
>   
>   	legacy_pic = &null_legacy_pic;
> +	swiotlb_force = SWIOTLB_FORCE;
>   
>   	cpuhp_setup_state(CPUHP_AP_ONLINE_DYN, "tdx:cpu_hotplug",
>   			  NULL, tdx_cpu_offline_prepare);
> diff --git a/arch/x86/mm/mem_encrypt.c b/arch/x86/mm/mem_encrypt.c
> index 5d7fbed73949..8385bc4565e9 100644
> --- a/arch/x86/mm/mem_encrypt.c
> +++ b/arch/x86/mm/mem_encrypt.c
> @@ -438,14 +438,11 @@ static void print_mem_encrypt_feature_info(void)
>   }
>   
>   /* Architecture __weak replacement functions */
> -void __init mem_encrypt_init(void)
> +void __init amd_mem_encrypt_init(void)
>   {
>   	if (!sme_me_mask)
>   		return;
>   
> -	/* Call into SWIOTLB to update the SWIOTLB DMA buffers */
> -	swiotlb_update_mem_attributes();
> -
>   	/*
>   	 * With SEV, we need to unroll the rep string I/O instructions,
>   	 * but SEV-ES supports them through the #VC handler.
> diff --git a/arch/x86/mm/mem_encrypt_common.c b/arch/x86/mm/mem_encrypt_common.c
> index 119a9056efbb..6fe44c6cb753 100644
> --- a/arch/x86/mm/mem_encrypt_common.c
> +++ b/arch/x86/mm/mem_encrypt_common.c
> @@ -10,6 +10,7 @@
>   #include <asm/mem_encrypt_common.h>
>   #include <linux/dma-mapping.h>
>   #include <linux/cc_platform.h>
> +#include <linux/swiotlb.h>
>   
>   /* Override for DMA direct allocation check - ARCH_HAS_FORCE_DMA_UNENCRYPTED */
>   bool force_dma_unencrypted(struct device *dev)
> @@ -24,3 +25,16 @@ bool force_dma_unencrypted(struct device *dev)
>   
>   	return false;
>   }
> +
> +/* Architecture __weak replacement functions */
> +void __init mem_encrypt_init(void)
> +{
> +	/*
> +	 * For TDX guest or SEV/SME, call into SWIOTLB to update
> +	 * the SWIOTLB DMA buffers
> +	 */
> +	if (sme_me_mask || cc_platform_has(CC_ATTR_GUEST_MEM_ENCRYPT))

Can't you just make this:

	if (cc_platform_has(CC_ATTR_MEM_ENCRYPT))

SEV will return true if sme_me_mask is not zero and TDX should only return true if it is TDX guest, right?

Thanks,
Tom

> +		swiotlb_update_mem_attributes();
> +
> +	amd_mem_encrypt_init();
> +}
>
```