Re: [RFC PATCH 08/15] x86/virt/tdx: Add interface to check Quoting availability

[Nikolay Borisov]

On 5/22/26 06:41, Xu Yilun wrote:
> From: Peter Fang <peter.fang@xxxxxxxxx>
>
> KVM needs to know if the Quoting extension is available to determine
> whether userspace must be involved in Quote generation.
>
> Since the Quote buffer is always created during Quoting extension
> bringup, checking whether the buffer exists is sufficient.
>
> Signed-off-by: Peter Fang <peter.fang@xxxxxxxxx>
> Signed-off-by: Xu Yilun <yilun.xu@xxxxxxxxxxxxxxx>
> ---
>   arch/x86/include/asm/tdx.h  |  2 ++
>   arch/x86/virt/vmx/tdx/tdx.c | 15 +++++++++++++++
>   2 files changed, 17 insertions(+)
>
> diff --git a/arch/x86/include/asm/tdx.h b/arch/x86/include/asm/tdx.h
> index 15eac89b0afb..7b257088aa1e 100644
> --- a/arch/x86/include/asm/tdx.h
> +++ b/arch/x86/include/asm/tdx.h
> @@ -176,6 +176,8 @@ struct tdx_vp {
>   	struct page **tdcx_pages;
>   };
>   
> +bool tdx_quote_enabled(void);
> +
>   static inline u64 mk_keyed_paddr(u16 hkid, struct page *page)
>   {
>   	u64 ret;
> diff --git a/arch/x86/virt/vmx/tdx/tdx.c b/arch/x86/virt/vmx/tdx/tdx.c
> index 9d04293394d7..b305fa5aab5c 100644
> --- a/arch/x86/virt/vmx/tdx/tdx.c
> +++ b/arch/x86/virt/vmx/tdx/tdx.c
> @@ -1213,6 +1213,21 @@ static inline u64 tdx_tdr_pa(struct tdx_td *td)
>   	return page_to_phys(td->tdr_page);
>   }
>   
> +/**
> + * tdx_quote_enabled() - Check whether TDX Quoting extension is available
> + *
> + * Return: %true if the Quoting extension is available, otherwise %false.
> + */
> +bool tdx_quote_enabled(void)

nit: Probably rename the function to tdx_quoting_ext_enabled or 
tdx_quote_ext_enabled, so it's abundantly clear it's about an extension 
and not the quoting functionality in general.


> +{
> +	/*
> +	 * No need for locking here. The quote buffer is initialized as part of
> +	 * core TDX bringup, which comes before KVM is ready for userspace.
> +	 */
> +	return !!quote_data.buf;

While this works it feels a bit like a hack, perhaps have a static 
boolean variable being set by the init code which is simply returned by 
this function.

> +}
> +EXPORT_SYMBOL_FOR_KVM(tdx_quote_enabled);
> +
>   #define HPAS_PER_PAGE			(PAGE_SIZE / sizeof(u64))
>   
>   static int tdx_quote_create_buf(unsigned int nr_pages, struct quote_data *qdata)