linux-kernel - Re: [PATCH v14 07/23] x86/virt/tdx: Add skeleton to enable TDX on demand

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Date:   Wed, 18 Oct 2023 10:57:36 +0300
From:   Nikolay Borisov <nik.borisov@...e.com>
To:     Kai Huang <kai.huang@...el.com>, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org
Cc:     x86@...nel.org, dave.hansen@...el.com,
        kirill.shutemov@...ux.intel.com, peterz@...radead.org,
        tony.luck@...el.com, tglx@...utronix.de, bp@...en8.de,
        mingo@...hat.com, hpa@...or.com, seanjc@...gle.com,
        pbonzini@...hat.com, rafael@...nel.org, david@...hat.com,
        dan.j.williams@...el.com, len.brown@...el.com, ak@...ux.intel.com,
        isaku.yamahata@...el.com, ying.huang@...el.com, chao.gao@...el.com,
        sathyanarayanan.kuppuswamy@...ux.intel.com, bagasdotme@...il.com,
        sagis@...gle.com, imammedo@...hat.com
Subject: Re: [PATCH v14 07/23] x86/virt/tdx: Add skeleton to enable TDX on
 demand

<snip>
> ---
>   arch/x86/include/asm/tdx.h  |   4 +
>   arch/x86/virt/vmx/tdx/tdx.c | 167 ++++++++++++++++++++++++++++++++++++
>   arch/x86/virt/vmx/tdx/tdx.h |  30 +++++++
>   3 files changed, 201 insertions(+)
>   create mode 100644 arch/x86/virt/vmx/tdx/tdx.h
> 
> diff --git a/arch/x86/include/asm/tdx.h b/arch/x86/include/asm/tdx.h
> index 984efd3114ed..3cfd64f8a2b5 100644
> --- a/arch/x86/include/asm/tdx.h
> +++ b/arch/x86/include/asm/tdx.h
> @@ -110,8 +110,12 @@ static inline u64 sc_retry(sc_func_t func, u64 fn,
>   #define seamcall_saved_ret(_fn, _args)	sc_retry(__seamcall_saved_ret, (_fn), (_args))
>   
>   bool platform_tdx_enabled(void);
> +int tdx_cpu_enable(void);
> +int tdx_enable(void);
>   #else
>   static inline bool platform_tdx_enabled(void) { return false; }
> +static inline int tdx_cpu_enable(void) { return -ENODEV; }
> +static inline int tdx_enable(void)  { return -ENODEV; }
>   #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 52fb14e0195f..36db33133cd5 100644
> --- a/arch/x86/virt/vmx/tdx/tdx.c
> +++ b/arch/x86/virt/vmx/tdx/tdx.c
> @@ -12,14 +12,24 @@
>   #include <linux/init.h>
>   #include <linux/errno.h>
>   #include <linux/printk.h>
> +#include <linux/cpu.h>
> +#include <linux/spinlock.h>
> +#include <linux/percpu-defs.h>
> +#include <linux/mutex.h>
>   #include <asm/msr-index.h>
>   #include <asm/msr.h>
>   #include <asm/tdx.h>
> +#include "tdx.h"
>   
>   static u32 tdx_global_keyid __ro_after_init;
>   static u32 tdx_guest_keyid_start __ro_after_init;
>   static u32 tdx_nr_guest_keyids __ro_after_init;
>   
> +static DEFINE_PER_CPU(bool, tdx_lp_initialized);
> +
> +static enum tdx_module_status_t tdx_module_status;
> +static DEFINE_MUTEX(tdx_module_lock);
> +
>   typedef void (*sc_err_func_t)(u64 fn, u64 err, struct tdx_module_args *args);
>   
>   static inline void seamcall_err(u64 fn, u64 err, struct tdx_module_args *args)
> @@ -72,6 +82,163 @@ 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))
>   
> +/*
> + * Do the module global initialization once and return its result.
> + * It can be done on any cpu.  It's always called with interrupts
> + * disabled.
> + */
> +static int try_init_module_global(void)
> +{

Any particular reason why this function is not called from the tdx 
module's tdx_init? It's global and must be called once when the module 
is initialised. Subsequently kvm which is supposed to call 
tdx_cpu_enable() must be sequenced _after_ tdx which shouldn't be that 
hard, no? This will eliminate the spinlock as well.

<snip>