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

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Message-ID: <dfb59553-2777-15ed-d523-6a7cc5b68e53@redhat.com>
Date:   Mon, 19 Jun 2023 15:00:11 +0200
From:   David Hildenbrand <david@...hat.com>
To:     Kai Huang <kai.huang@...el.com>, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org
Cc:     linux-mm@...ck.org, dave.hansen@...el.com,
        kirill.shutemov@...ux.intel.com, tony.luck@...el.com,
        peterz@...radead.org, tglx@...utronix.de, seanjc@...gle.com,
        pbonzini@...hat.com, dan.j.williams@...el.com,
        rafael.j.wysocki@...el.com, ying.huang@...el.com,
        reinette.chatre@...el.com, len.brown@...el.com, ak@...ux.intel.com,
        isaku.yamahata@...el.com, chao.gao@...el.com,
        sathyanarayanan.kuppuswamy@...ux.intel.com, bagasdotme@...il.com,
        sagis@...gle.com, imammedo@...hat.com
Subject: Re: [PATCH v11 06/20] x86/virt/tdx: Handle SEAMCALL running out of
 entropy error

On 04.06.23 16:27, Kai Huang wrote:
> Certain SEAMCALL leaf functions may return error due to running out of
> entropy, in which case the SEAMCALL should be retried as suggested by
> the TDX spec.
> 
> Handle this case in SEAMCALL common function.  Mimic the existing
> rdrand_long() to retry RDRAND_RETRY_LOOPS times.
> 
> Signed-off-by: Kai Huang <kai.huang@...el.com>
> ---
> 
> v10 -> v11:
>   - New patch
> 
> ---
>   arch/x86/virt/vmx/tdx/tdx.c | 15 ++++++++++++++-
>   arch/x86/virt/vmx/tdx/tdx.h | 17 +++++++++++++++++
>   2 files changed, 31 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/x86/virt/vmx/tdx/tdx.c b/arch/x86/virt/vmx/tdx/tdx.c
> index e82713dd5d54..e62e978eba1b 100644
> --- a/arch/x86/virt/vmx/tdx/tdx.c
> +++ b/arch/x86/virt/vmx/tdx/tdx.c
> @@ -15,6 +15,7 @@
>   #include <linux/smp.h>
>   #include <asm/msr-index.h>
>   #include <asm/msr.h>
> +#include <asm/archrandom.h>
>   #include <asm/tdx.h>
>   #include "tdx.h"
>   
> @@ -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."

> +	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>

-- 
Cheers,

David / dhildenb