linux-kernel - Re: [PATCH v12 06/22] x86/virt/tdx: Handle SEAMCALL running out of entropy error

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Date:   Wed, 28 Jun 2023 15:02:56 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Kai Huang <kai.huang@...el.com>
Cc:     linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        linux-mm@...ck.org, x86@...nel.org, dave.hansen@...el.com,
        kirill.shutemov@...ux.intel.com, tony.luck@...el.com,
        tglx@...utronix.de, bp@...en8.de, mingo@...hat.com, hpa@...or.com,
        seanjc@...gle.com, pbonzini@...hat.com, david@...hat.com,
        dan.j.williams@...el.com, rafael.j.wysocki@...el.com,
        ashok.raj@...el.com, reinette.chatre@...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, nik.borisov@...e.com,
        bagasdotme@...il.com, sagis@...gle.com, imammedo@...hat.com
Subject: Re: [PATCH v12 06/22] x86/virt/tdx: Handle SEAMCALL running out of
 entropy error

On Tue, Jun 27, 2023 at 02:12:36AM +1200, Kai Huang wrote:

>  	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 rdrand_long() retry behavior.

Yeah, except that doesn't have preemption disabled.. you do.

> +	 */
> +	do {
> +		sret = __seamcall(fn, rcx, rdx, r8, r9, out);
> +	} while (sret == TDX_RND_NO_ENTROPY && --retry);
> +
>  	put_cpu();