linux-kernel - Re: [PATCH v11 013/113] x86/cpu: Add helper functions to allocate/free TDX private host key id

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Date:   Fri, 13 Jan 2023 14:47:12 +0200
From:   Zhi Wang <zhi.wang.linux@...il.com>
To:     isaku.yamahata@...el.com
Cc:     kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        isaku.yamahata@...il.com, Paolo Bonzini <pbonzini@...hat.com>,
        erdemaktas@...gle.com, Sean Christopherson <seanjc@...gle.com>,
        Sagi Shahar <sagis@...gle.com>,
        David Matlack <dmatlack@...gle.com>
Subject: Re: [PATCH v11 013/113] x86/cpu: Add helper functions to
 allocate/free TDX private host key id

On Thu, 12 Jan 2023 08:31:21 -0800
isaku.yamahata@...el.com wrote:

> From: Isaku Yamahata <isaku.yamahata@...el.com>
> 
> TDX private host key id (HKID) is assigned to guest TD.  The memory
> controller encrypts guest TD memory with the assigned TDX HKID.  Add
> helper functions to allocate/free TDX private HKID so that TDX KVM can
> manage it.
> 
> Also export the global TDX private HKID that is used to encrypt TDX
> module, its memory and some dynamic data (TDR).  When VMM releasing
> encrypted page to reuse it, the page needs to be flushed with the used
> HKID.  VMM needs the global TDX private HKID to flush such pages.
> 
> Signed-off-by: Isaku Yamahata <isaku.yamahata@...el.com>
> ---
>  arch/x86/include/asm/tdx.h  | 12 ++++++++++++
>  arch/x86/virt/vmx/tdx/tdx.c | 35 +++++++++++++++++++++++++++++++++++
>  2 files changed, 47 insertions(+)
> 
> diff --git a/arch/x86/include/asm/tdx.h b/arch/x86/include/asm/tdx.h
> index 0f71d3856ede..ed9cf61ff8b4 100644
> --- a/arch/x86/include/asm/tdx.h
> +++ b/arch/x86/include/asm/tdx.h
> @@ -107,11 +107,23 @@ static inline long tdx_kvm_hypercall(unsigned int
> nr, unsigned long p1, #ifdef CONFIG_INTEL_TDX_HOST
>  bool platform_tdx_enabled(void);
>  int tdx_enable(void);
> +/*
> + * Key id globally used by TDX module: TDX module maps TDR with this
> TDX global
> + * key id.  TDR includes key id assigned to the TD.  Then TDX module
> maps other
> + * TD-related pages with the assigned key id.  TDR requires this TDX
> global key
> + * id for cache flush unlike other TD-related pages.
> + */
> +extern u32 tdx_global_keyid __read_mostly;
> +int tdx_keyid_alloc(void);
> +void tdx_keyid_free(int keyid);
> +
>  u64 __seamcall(u64 op, u64 rcx, u64 rdx, u64 r8, u64 r9,
>  	       struct tdx_module_output *out);
>  #else	/* !CONFIG_INTEL_TDX_HOST */
>  static inline bool platform_tdx_enabled(void) { return false; }
>  static inline int tdx_enable(void)  { return -EINVAL; }
> +static inline int tdx_keyid_alloc(void) { return -EOPNOTSUPP; }
> +static inline void tdx_keyid_free(int keyid) { }
>  #endif	/* CONFIG_INTEL_TDX_HOST */
>  
>  #endif /* !__ASSEMBLY__ */
> diff --git a/arch/x86/virt/vmx/tdx/tdx.c b/arch/x86/virt/vmx/tdx/tdx.c
> index eba7e62cebec..d18ab5c4d447 100644
> --- a/arch/x86/virt/vmx/tdx/tdx.c
> +++ b/arch/x86/virt/vmx/tdx/tdx.c
> @@ -51,6 +51,10 @@ static DEFINE_MUTEX(tdx_module_lock);
>  /* All TDX-usable memory regions */
>  static LIST_HEAD(tdx_memlist);
>  
> +/* TDX module global KeyID.  Used in TDH.SYS.CONFIG ABI. */
> +u32 tdx_global_keyid __read_mostly;
> +EXPORT_SYMBOL_GPL(tdx_global_keyid);
> +
>  /*
>   * tdx_keyid_start and nr_tdx_keyids indicate that TDX is uninitialized.
>   * This is used in TDX initialization error paths to take it from
> @@ -132,6 +136,31 @@ static struct notifier_block tdx_memory_nb = {
>  	.notifier_call = tdx_memory_notifier,
>  };
>  
> +/* TDX KeyID pool */
> +static DEFINE_IDA(tdx_keyid_pool);
> +
> +int tdx_keyid_alloc(void)
> +{
> +	if (WARN_ON_ONCE(!tdx_keyid_start || !nr_tdx_keyids))
> +		return -EINVAL;

Better mention that tdx_keyid_start and nr_tdx_keyids are defined in
another patches.

> +
> +	/* The first keyID is reserved for the global key. */
> +	return ida_alloc_range(&tdx_keyid_pool, tdx_keyid_start + 1,
> +			       tdx_keyid_start + nr_tdx_keyids - 1,
> +			       GFP_KERNEL);
> +}
> +EXPORT_SYMBOL_GPL(tdx_keyid_alloc);
> +
> +void tdx_keyid_free(int keyid)
> +{
> +	/* keyid = 0 is reserved. */
> +	if (WARN_ON_ONCE(keyid <= 0))
> +		return;
> +
> +	ida_free(&tdx_keyid_pool, keyid);
> +}
> +EXPORT_SYMBOL_GPL(tdx_keyid_free);
> +
>  static int __init tdx_init(void)
>  {
>  	int err;
> @@ -1161,6 +1190,12 @@ static int init_tdx_module(void)
>  	if (ret)
>  		goto out_free_pamts;
>  
> +	/*
> +	 * Reserve the first TDX KeyID as global KeyID to protect
> +	 * TDX module metadata.
> +	 */
> +	tdx_global_keyid = tdx_keyid_start;
> +
>  	/* Initialize TDMRs to complete the TDX module initialization */
>  	ret = init_tdmrs(&tdmr_list);
>  	if (ret)