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Date:   Wed, 9 Mar 2022 12:07:22 -0800
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To:     "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
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References: <20220302142806.51844-1-kirill.shutemov@linux.intel.com>
 <20220302142806.51844-28-kirill.shutemov@linux.intel.com>
From:   Dave Hansen <dave.hansen@intel.com>
Subject: Re: [PATCHv5 27/30] x86/kvm: Use bounce buffers for TD guest
In-Reply-To: <20220302142806.51844-28-kirill.shutemov@linux.intel.com>
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On 3/2/22 06:28, Kirill A. Shutemov wrote:
> --- a/arch/x86/coco/tdx.c
> +++ b/arch/x86/coco/tdx.c
> @@ -5,6 +5,7 @@
>  #define pr_fmt(fmt)     "tdx: " fmt
>  
>  #include <linux/cpufeature.h>
> +#include <linux/swiotlb.h>
>  #include <asm/coco.h>
>  #include <asm/tdx.h>
>  #include <asm/vmx.h>
> @@ -627,5 +628,7 @@ void __init tdx_early_init(void)
>  	x86_platform.guest.enc_tlb_flush_required = tdx_tlb_flush_required;
>  	x86_platform.guest.enc_status_change_finish = tdx_enc_status_changed;
>  
> +	swiotlb_force = SWIOTLB_FORCE;
> +
>  	pr_info("Guest detected\n");
>  }

AMD currently does:

        if (cc_platform_has(CC_ATTR_GUEST_MEM_ENCRYPT))
                swiotlb_force = SWIOTLB_FORCE;

which somewhat begs the question of why we can't do the

	swiotlb_force = SWIOTLB_FORCE;

thing in:

void __init mem_encrypt_init(void)
{
        if (!cc_platform_has(CC_ATTR_MEM_ENCRYPT))
                return;

/// Here

I recall there being a reason for this.  But I don't see any mention in
the changelog.