Re: [PATCH 1/2] x86/virt/tdx: Drop tdx_clflush_*()

[Yan Zhao]

Reviewed-by: Yan Zhao <yan.y.zhao@xxxxxxxxx>

Just some nits to the commit log. Free free to ignore.

On Tue, Sep 22, 2026 at 01:52:14PM -0700, Rick Edgecombe wrote:
> The TDX module exposes a bit (CLFLUSH_BEFORE_ALLOC) to say whether it
> requires some memory to be flushed from the cache before being handed
Drop "some"?

> to the TDX module.
> 
> During the initial TDX upstreaming, it was decided it would be simplest
> to just always flush in these cases, rather than checking for the bit and
"in these cases" is ambiguous.

> having conditional logic. So currently the kernel flushes in several
> places when handing memory to the TDX module.
>
> In practice this bit has never been set by any TDX module, so flushing
> is unneeded. Going forward the TDX docs will be updated to clarify that
"Going forward, ...".

> CLFLUSH_BEFORE_ALLOC will never be set in any future TDX module either.
> 
> So make code even simpler by just deleting all the CLFLUSH_BEFORE_ALLOC
> handling.
> 
> AI was used to review the change.
> 
> Signed-off-by: Rick Edgecombe <rick.p.edgecombe@xxxxxxxxx>
> ---
>  arch/x86/virt/vmx/tdx/tdx.c | 23 -----------------------
>  1 file changed, 23 deletions(-)
> 
> diff --git a/arch/x86/virt/vmx/tdx/tdx.c b/arch/x86/virt/vmx/tdx/tdx.c
> index 1b9ff749dd8e0..8f9d3588f200f 100644
> --- a/arch/x86/virt/vmx/tdx/tdx.c
> +++ b/arch/x86/virt/vmx/tdx/tdx.c
> @@ -1619,22 +1619,6 @@ static inline u64 tdx_tdr_pa(struct tdx_td *td)
>  	return page_to_phys(td->tdr_page);
>  }
>  
> -/*
> - * The TDX module exposes a CLFLUSH_BEFORE_ALLOC bit to specify whether
> - * a CLFLUSH of pages is required before handing them to the TDX module.
> - * Be conservative and make the code simpler by doing the CLFLUSH
> - * unconditionally.
> - */
> -static void tdx_clflush_page(struct page *page)
> -{
> -	clflush_cache_range(page_to_virt(page), PAGE_SIZE);
> -}
> -
> -static void tdx_clflush_pfn(kvm_pfn_t pfn)
> -{
> -	clflush_cache_range(__va(PFN_PHYS(pfn)), PAGE_SIZE);
> -}
> -
>  static int pg_level_to_tdx_sept_level(enum pg_level level)
>  {
>  	WARN_ON_ONCE(level == PG_LEVEL_NONE);
> @@ -1656,7 +1640,6 @@ u64 tdh_mng_addcx(struct tdx_td *td, struct page *tdcs_page)
>  		.rdx = tdx_tdr_pa(td),
>  	};
>  
> -	tdx_clflush_page(tdcs_page);
>  	return seamcall(TDH_MNG_ADDCX, &args);
>  }
>  EXPORT_SYMBOL_FOR_KVM(tdh_mng_addcx);
> @@ -1672,7 +1655,6 @@ u64 tdh_mem_page_add(struct tdx_td *td, u64 gpa, kvm_pfn_t pfn, struct page *sou
>  	};
>  	u64 ret;
>  
> -	tdx_clflush_pfn(pfn);
>  	ret = seamcall_ret(TDH_MEM_PAGE_ADD, &args);
>  
>  	*ext_err1 = args.rcx;
> @@ -1692,7 +1674,6 @@ u64 tdh_mem_sept_add(struct tdx_td *td, u64 gpa, enum pg_level level,
>  	};
>  	u64 ret;
>  
> -	tdx_clflush_page(page);
>  	ret = seamcall_ret(TDH_MEM_SEPT_ADD, &args);
>  
>  	*ext_err1 = args.rcx;
> @@ -1709,7 +1690,6 @@ u64 tdh_vp_addcx(struct tdx_vp *vp, struct page *tdcx_page)
>  		.rdx = vp->tdvpr_pa,
>  	};
>  
> -	tdx_clflush_page(tdcx_page);
>  	return seamcall(TDH_VP_ADDCX, &args);
>  }
>  EXPORT_SYMBOL_FOR_KVM(tdh_vp_addcx);
> @@ -1724,7 +1704,6 @@ u64 tdh_mem_page_aug(struct tdx_td *td, u64 gpa, enum pg_level level,
>  	};
>  	u64 ret;
>  
> -	tdx_clflush_pfn(pfn);
>  	ret = seamcall_ret(TDH_MEM_PAGE_AUG, &args);
>  
>  	*ext_err1 = args.rcx;
> @@ -1769,7 +1748,6 @@ u64 tdh_mng_create(struct tdx_td *td, u16 hkid)
>  		.rdx = hkid,
>  	};
>  
> -	tdx_clflush_page(td->tdr_page);
>  	return seamcall(TDH_MNG_CREATE, &args);
>  }
>  EXPORT_SYMBOL_FOR_KVM(tdh_mng_create);
> @@ -1781,7 +1759,6 @@ u64 tdh_vp_create(struct tdx_td *td, struct tdx_vp *vp)
>  		.rdx = tdx_tdr_pa(td),
>  	};
>  
> -	tdx_clflush_page(vp->tdvpr_page);
>  	return seamcall(TDH_VP_CREATE, &args);
>  }
>  EXPORT_SYMBOL_FOR_KVM(tdh_vp_create);
> -- 
> 2.55.0
>