linux-kernel - Re: [PATCH v8 019/103] x86/cpu: Add helper functions to allocate/free TDX private host key id

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Message-ID: <20220830071748.dtr2h3x7dvblkc4b@yy-desk-7060>
Date:   Tue, 30 Aug 2022 15:17:48 +0800
From:   Yuan Yao <yuan.yao@...ux.intel.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>
Subject: Re: [PATCH v8 019/103] x86/cpu: Add helper functions to
 allocate/free TDX private host key id

On Sun, Aug 07, 2022 at 03:01:04PM -0700, isaku.yamahata@...el.com wrote:
> From: Isaku Yamahata <isaku.yamahata@...el.com>
>
> TDX private host key id is assigned to guest TD.  The memory controller
> encrypts guest TD memory with the assigned TDX private host key id (HIKD).
> Add helper functions to allocate/free TDX private host key id so that TDX
> KVM manage it.
>
> Also export the global TDX private host key id 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 host
> key id.  VMM needs the global TDX private host key id to flush such pages
> TDX module accesses with the global TDX private host key id.
>
> 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 c887618e3cec..a32e8881e758 100644
> --- a/arch/x86/include/asm/tdx.h
> +++ b/arch/x86/include/asm/tdx.h
> @@ -144,6 +144,16 @@ struct tdsysinfo_struct {
>  bool platform_tdx_enabled(void);
>  int tdx_init(void);
>  const struct tdsysinfo_struct *tdx_get_sysinfo(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 */
> @@ -151,6 +161,8 @@ static inline bool platform_tdx_enabled(void) { return false; }
>  static inline int tdx_init(void)  { return -ENODEV; }
>  struct tdsysinfo_struct;
>  static inline const struct tdsysinfo_struct *tdx_get_sysinfo(void) { return NULL; }
> +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 918e79159bbf..2168e6133d45 100644
> --- a/arch/x86/virt/vmx/tdx/tdx.c
> +++ b/arch/x86/virt/vmx/tdx/tdx.c
> @@ -56,7 +56,8 @@ static struct cmr_info tdx_cmr_array[MAX_CMRS] __aligned(CMR_INFO_ARRAY_ALIGNMEN
>  static int tdx_cmr_num;
>
>  /* TDX module global KeyID.  Used in TDH.SYS.CONFIG ABI. */
> -static u32 tdx_global_keyid;
> +u32 tdx_global_keyid __read_mostly;
> +EXPORT_SYMBOL_GPL(tdx_global_keyid);
>
>  /* Detect whether CPU supports SEAM */
>  static int detect_seam(void)
> @@ -80,6 +81,31 @@ static int detect_seam(void)
>  	return 0;
>  }
>
> +/* TDX KeyID pool */
> +static DEFINE_IDA(tdx_keyid_pool);
> +
> +int tdx_keyid_alloc(void)
> +{
> +	if (WARN_ON_ONCE(!tdx_keyid_start || !tdx_keyid_num))
> +		return -EINVAL;
> +
> +	/* The first keyID is reserved for the global key. */
> +	return ida_alloc_range(&tdx_keyid_pool, tdx_keyid_start + 1,
> +			       tdx_keyid_start + tdx_keyid_num - 1,
> +			       GFP_KERNEL);
> +}
> +EXPORT_SYMBOL_GPL(tdx_keyid_alloc);
> +
> +void tdx_keyid_free(int keyid)
> +{
> +	/* keyid = 0 is reserved. */
> +	if (!keyid || keyid <= 0)

keyid <=0 covers !keyid.

> +		return;
> +
> +	ida_free(&tdx_keyid_pool, keyid);
> +}
> +EXPORT_SYMBOL_GPL(tdx_keyid_free);
> +
>  static int detect_tdx_keyids(void)
>  {
>  	u64 keyid_part;
> --
> 2.25.1
>