linux-kernel - Re: [PATCH v13 05/22] x86/virt/tdx: Handle SEAMCALL no entropy error in common code

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Message-ID: <14e8f19b93f3e0eb381061320b47a8c4a048c9cd.camel@intel.com>
Date:   Mon, 11 Sep 2023 11:41:37 +0000
From:   "Huang, Kai" <kai.huang@...el.com>
To:     "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "Hansen, Dave" <dave.hansen@...el.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
CC:     "Raj, Ashok" <ashok.raj@...el.com>,
        "Luck, Tony" <tony.luck@...el.com>,
        "david@...hat.com" <david@...hat.com>,
        "bagasdotme@...il.com" <bagasdotme@...il.com>,
        "ak@...ux.intel.com" <ak@...ux.intel.com>,
        "Wysocki, Rafael J" <rafael.j.wysocki@...el.com>,
        "kirill.shutemov@...ux.intel.com" <kirill.shutemov@...ux.intel.com>,
        "Chatre, Reinette" <reinette.chatre@...el.com>,
        "Christopherson,, Sean" <seanjc@...gle.com>,
        "pbonzini@...hat.com" <pbonzini@...hat.com>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "Yamahata, Isaku" <isaku.yamahata@...el.com>,
        "nik.borisov@...e.com" <nik.borisov@...e.com>,
        "hpa@...or.com" <hpa@...or.com>,
        "peterz@...radead.org" <peterz@...radead.org>,
        "Shahar, Sagi" <sagis@...gle.com>,
        "imammedo@...hat.com" <imammedo@...hat.com>,
        "bp@...en8.de" <bp@...en8.de>, "Gao, Chao" <chao.gao@...el.com>,
        "Brown, Len" <len.brown@...el.com>,
        "sathyanarayanan.kuppuswamy@...ux.intel.com" 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>,
        "Huang, Ying" <ying.huang@...el.com>,
        "Williams, Dan J" <dan.j.williams@...el.com>,
        "x86@...nel.org" <x86@...nel.org>
Subject: Re: [PATCH v13 05/22] x86/virt/tdx: Handle SEAMCALL no entropy error
 in common code

On Fri, 2023-09-08 at 09:21 -0700, Dave Hansen wrote:
> On 8/25/23 05:14, Kai Huang wrote:
> > Some SEAMCALLs use the RDRAND hardware and can fail for the same reasons
> > as RDRAND.  Use the kernel RDRAND retry logic for them.
> > 
> > There are three __seamcall*() variants.  Add a macro to do the SEAMCALL
> > retry in the common code and define a wrapper for each __seamcall*()
> > variant.
> > 
> > Signed-off-by: Kai Huang <kai.huang@...el.com>
> > ---
> > 
> > v12 -> v13:
> >  - New implementation due to TDCALL assembly series.
> > 
> > ---
> >  arch/x86/include/asm/tdx.h | 27 +++++++++++++++++++++++++++
> >  1 file changed, 27 insertions(+)
> > 
> > diff --git a/arch/x86/include/asm/tdx.h b/arch/x86/include/asm/tdx.h
> > index a252328734c7..cfae8b31a2e9 100644
> > --- a/arch/x86/include/asm/tdx.h
> > +++ b/arch/x86/include/asm/tdx.h
> > @@ -24,6 +24,11 @@
> >  #define TDX_SEAMCALL_GP			(TDX_SW_ERROR | X86_TRAP_GP)
> >  #define TDX_SEAMCALL_UD			(TDX_SW_ERROR | X86_TRAP_UD)
> >  
> > +/*
> > + * TDX module SEAMCALL leaf function error codes
> > + */
> > +#define TDX_RND_NO_ENTROPY	0x8000020300000000ULL
> > +
> >  #ifndef __ASSEMBLY__
> >  
> >  /*
> > @@ -82,6 +87,28 @@ u64 __seamcall(u64 fn, struct tdx_module_args *args);
> >  u64 __seamcall_ret(u64 fn, struct tdx_module_args *args);
> >  u64 __seamcall_saved_ret(u64 fn, struct tdx_module_args *args);
> >  
> > +#include <asm/archrandom.h>
> > +
> > +#define SEAMCALL_NO_ENTROPY_RETRY(__seamcall_func, __fn, __args)	\
> > +({									\
> > +	int ___retry = RDRAND_RETRY_LOOPS;				\
> > +	u64 ___sret;							\
> > +									\
> > +	do {								\
> > +		___sret = __seamcall_func((__fn), (__args));		\
> > +	} while (___sret == TDX_RND_NO_ENTROPY && --___retry);		\
> > +	___sret;							\
> > +})
> 
> This is a *LOT* less eye-bleedy if you do it without macros:
> 
> 
> typedef u64 (*sc_func_t)(u64 fn, struct tdx_module_args *args);
> 
> static inline
> u64 sc_retry(sc_func_t func, u64 fn, struct tdx_module_args *args)
> {
>         int retry = RDRAND_RETRY_LOOPS;
>         u64 ret;
> 
>         do {
>                 ret = func(fn, args);
>         } while (ret == TDX_RND_NO_ENTROPY && --retry);
> 
>         return ret;
> }
> 
> #define seamcall(_fn, _args)           sc_retry(_seamcall,
> (_fn), (_args))
> #define seamcall_ret(_fn, _args)       sc_retry(_seamcall_ret,
> (_fn), (_args))
> #define seamcall_saved_ret(_fn, _args) sc_retry(_seamcall_saved_ret,
> (_fn), (_args))
> 
> The compiler can figure it out and avoid making func() an indirect call
> since it knows the call location at compile time.

Indirect call was a concern when I was implementing those.  I didn't know for 
sure that the compiler can avoid it.  I'll change to use above.  Thanks!

> 
> You can also do the seamcall() #define as a static inline, but it does
> take up more screen real estate.  Oh, and going a wee bit over 80
> columns is OK for those #defines.

Yes I verified the checkpatch.pl wouldn't complain if the #define exceeded 80
characters in one line.  I'll use #define.  Thanks!