linux-kernel - Re: [PATCH v17 015/116] x86/cpu: Add helper functions to allocate/free TDX private host key id

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Message-ID: <35cd1aad-87b6-4606-9811-ab56530cf896@intel.com>
Date:   Wed, 15 Nov 2023 15:35:11 +0800
From:   Chenyi Qiang <chenyi.qiang@...el.com>
To:     <isaku.yamahata@...el.com>, <kvm@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>
CC:     <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>,
        Kai Huang <kai.huang@...el.com>,
        Zhi Wang <zhi.wang.linux@...il.com>, <chen.bo@...el.com>,
        <hang.yuan@...el.com>, <tina.zhang@...el.com>
Subject: Re: [PATCH v17 015/116] x86/cpu: Add helper functions to
 allocate/free TDX private host key id



On 11/7/2023 10:55 PM, isaku.yamahata@...el.com wrote:
> From: Isaku Yamahata <isaku.yamahata@...el.com>
> 
> Add helper functions to allocate/free TDX private host key id (HKID), and
> export the global TDX HKID.
> 
> The memory controller encrypts TDX memory with the assigned TDX HKIDs.  The
> global TDX HKID is to encrypt the TDX module, its memory, and some dynamic
> data (TDR).  The private TDX HKID is assigned to guest TD to encrypt guest
> memory and the related data.  When VMM releases an encrypted page for
> reuse, the page needs a cache flush with the used HKID.  VMM needs the
> global TDX HKID and the private TDX HKIDs to flush encrypted pages.
> 
> Signed-off-by: Isaku Yamahata <isaku.yamahata@...el.com>
> ---
>  arch/x86/include/asm/tdx.h  | 12 ++++++++++++
>  arch/x86/virt/vmx/tdx/tdx.c | 28 +++++++++++++++++++++++++++-
>  2 files changed, 39 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/x86/include/asm/tdx.h b/arch/x86/include/asm/tdx.h
> index b7cfdf084860..3b648f290af3 100644
> --- a/arch/x86/include/asm/tdx.h
> +++ b/arch/x86/include/asm/tdx.h
> @@ -114,6 +114,16 @@ int tdx_cpu_enable(void);
>  int tdx_enable(void);
>  void tdx_reset_memory(void);
>  bool tdx_is_private_mem(unsigned long phys);
> +
> +/*
> + * 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;
> +int tdx_guest_keyid_alloc(void);
> +void tdx_guest_keyid_free(int keyid);
>  #else
>  static inline u64 __seamcall(u64 fn, struct tdx_module_args *args)
>  {
> @@ -132,6 +142,8 @@ static inline int tdx_cpu_enable(void) { return -ENODEV; }
>  static inline int tdx_enable(void)  { return -ENODEV; }
>  static inline void tdx_reset_memory(void) { }
>  static inline bool tdx_is_private_mem(unsigned long phys) { return false; }
> +static inline int tdx_guest_keyid_alloc(void) { return -EOPNOTSUPP; }
> +static inline void tdx_guest_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 38ec6815a42a..c01cbfc81fbb 100644
> --- a/arch/x86/virt/vmx/tdx/tdx.c
> +++ b/arch/x86/virt/vmx/tdx/tdx.c
> @@ -37,7 +37,8 @@
>  #include <asm/tdx.h>
>  #include "tdx.h"
>  
> -static u32 tdx_global_keyid __ro_after_init;
> +u32 tdx_global_keyid __ro_after_init;
> +EXPORT_SYMBOL_GPL(tdx_global_keyid);
>  static u32 tdx_guest_keyid_start __ro_after_init;
>  static u32 tdx_nr_guest_keyids __ro_after_init;
>  
> @@ -105,6 +106,31 @@ static inline int sc_retry_prerr(sc_func_t func, sc_err_func_t err_func,
>  #define seamcall_prerr_ret(__fn, __args)					\
>  	sc_retry_prerr(__seamcall_ret, seamcall_err_ret, (__fn), (__args))
>  
> +/* TDX KeyID pool */
> +static DEFINE_IDA(tdx_guest_keyid_pool);
> +
> +int tdx_guest_keyid_alloc(void)
> +{
> +	if (WARN_ON_ONCE(!tdx_guest_keyid_start || !tdx_nr_guest_keyids))
> +		return -EINVAL;
> +
> +	/* The first keyID is reserved for the global key. */
> +	return ida_alloc_range(&tdx_guest_keyid_pool, tdx_guest_keyid_start + 1,

Per
https://lore.kernel.org/all/121aab11b48b4e6550cfe6d23b4daab744ee2076.1697532085.git.kai.huang@intel.com/
tdx_guest_keyid_start has already reserved the first keyID for global
key, I think we don't need to reserve another one here.

> +			       tdx_guest_keyid_start + tdx_nr_guest_keyids - 1,
> +			       GFP_KERNEL);
> +}
> +EXPORT_SYMBOL_GPL(tdx_guest_keyid_alloc);
> +
> +void tdx_guest_keyid_free(int keyid)
> +{
> +	/* keyid = 0 is reserved. */
> +	if (WARN_ON_ONCE(keyid <= 0))
> +		return;
> +
> +	ida_free(&tdx_guest_keyid_pool, keyid);
> +}
> +EXPORT_SYMBOL_GPL(tdx_guest_keyid_free);
> +
>  /*
>   * Do the module global initialization once and return its result.
>   * It can be done on any cpu.  It's always called with interrupts