linux-kernel - Re: [PATCH v11 06/20] x86/virt/tdx: Handle SEAMCALL running out of entropy error

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Date:   Tue, 20 Jun 2023 10:39:02 +0000
From:   "Huang, Kai" <kai.huang@...el.com>
To:     "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "david@...hat.com" <david@...hat.com>
CC:     "Hansen, Dave" <dave.hansen@...el.com>,
        "Luck, Tony" <tony.luck@...el.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>,
        "Christopherson,, Sean" <seanjc@...gle.com>,
        "Chatre, Reinette" <reinette.chatre@...el.com>,
        "pbonzini@...hat.com" <pbonzini@...hat.com>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "Yamahata, Isaku" <isaku.yamahata@...el.com>,
        "peterz@...radead.org" <peterz@...radead.org>,
        "Shahar, Sagi" <sagis@...gle.com>,
        "imammedo@...hat.com" <imammedo@...hat.com>,
        "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>
Subject: Re: [PATCH v11 06/20] x86/virt/tdx: Handle SEAMCALL running out of
 entropy error


> > @@ -33,12 +34,24 @@ static int __always_unused seamcall(u64 fn, u64 rcx, u64 rdx, u64 r8, u64 r9,
> >   				    struct tdx_module_output *out)
> >   {
> >   	int cpu, ret = 0;
> > +	int retry;
> >   	u64 sret;
> >   
> >   	/* Need a stable CPU id for printing error message */
> >   	cpu = get_cpu();
> >   
> > -	sret = __seamcall(fn, rcx, rdx, r8, r9, out);
> > +	/*
> > +	 * Certain SEAMCALL leaf functions may return error due to
> > +	 * running out of entropy, in which case the SEAMCALL should
> > +	 * be retried.  Handle this in SEAMCALL common function.
> > +	 *
> > +	 * Mimic the existing rdrand_long() to retry
> > +	 * RDRAND_RETRY_LOOPS times.
> > +	 */
> > +	retry = RDRAND_RETRY_LOOPS;
> 
> Nit: I'd just do a "int retry = RDRAND_RETRY_LOOPS" and simplify this 
> comment to "Mimic rdrand_long() retry behavior."

OK will do.

But I think you are talking about replacing the second paragraph but not the
entire comment?

> 
> > +	do {
> > +		sret = __seamcall(fn, rcx, rdx, r8, r9, out);
> > +	} while (sret == TDX_RND_NO_ENTROPY && --retry);
> >   
> >   	/* Save SEAMCALL return code if the caller wants it */
> >   	if (seamcall_ret)
> > diff --git a/arch/x86/virt/vmx/tdx/tdx.h b/arch/x86/virt/vmx/tdx/tdx.h
> > index 48ad1a1ba737..55dbb1b8c971 100644
> > --- a/arch/x86/virt/vmx/tdx/tdx.h
> > +++ b/arch/x86/virt/vmx/tdx/tdx.h
> > @@ -4,6 +4,23 @@
> >   
> >   #include <linux/types.h>
> >   
> > +/*
> > + * This file contains both macros and data structures defined by the TDX
> > + * architecture and Linux defined software data structures and functions.
> > + * The two should not be mixed together for better readability.  The
> > + * architectural definitions come first.
> > + */
> > +
> > +/*
> > + * TDX SEAMCALL error codes
> > + */
> > +#define TDX_RND_NO_ENTROPY	0x8000020300000000ULL
> > +
> > +/*
> > + * Do not put any hardware-defined TDX structure representations below
> > + * this comment!
> > + */
> > +
> >   struct tdx_module_output;
> >   u64 __seamcall(u64 fn, u64 rcx, u64 rdx, u64 r8, u64 r9,
> >   	       struct tdx_module_output *out);
> 
> In general, LGTM
> 
> Reviewed-by: David Hildenbrand <david@...hat.com>

Thanks!