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Message-ID: <90ff7c36-9b2e-c791-dc26-3644b9ff20df@intel.com>
Date:   Tue, 20 Jun 2023 16:34:08 -0700
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Subject: Re: [PATCH v8 1/2] x86/tdx: Retry TDVMCALL_MAP_GPA() when needed
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To:     Dexuan Cui <decui@microsoft.com>, ak@linux.intel.com,
        arnd@arndb.de, bp@alien8.de, brijesh.singh@amd.com,
        dan.j.williams@intel.com, dave.hansen@linux.intel.com,
        haiyangz@microsoft.com, hpa@zytor.com, jane.chu@oracle.com,
        kirill.shutemov@linux.intel.com, kys@microsoft.com,
        linux-arch@vger.kernel.org, linux-hyperv@vger.kernel.org,
        luto@kernel.org, mingo@redhat.com, peterz@infradead.org,
        rostedt@goodmis.org, sathyanarayanan.kuppuswamy@linux.intel.com,
        seanjc@google.com, tglx@linutronix.de, tony.luck@intel.com,
        wei.liu@kernel.org, x86@kernel.org, mikelley@microsoft.com
Cc:     linux-kernel@vger.kernel.org, Tianyu.Lan@microsoft.com,
        rick.p.edgecombe@intel.com
References: <20230620154830.25442-1-decui@microsoft.com>
 <20230620154830.25442-2-decui@microsoft.com>
From:   Dave Hansen <dave.hansen@intel.com>
In-Reply-To: <20230620154830.25442-2-decui@microsoft.com>
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Precedence: bulk

On 6/20/23 08:48, Dexuan Cui wrote:
> -static bool tdx_enc_status_changed(unsigned long vaddr, int numpages, bool enc)
> +static bool tdx_map_gpa(phys_addr_t start, phys_addr_t end, bool enc)
>  {
> -	phys_addr_t start = __pa(vaddr);
> -	phys_addr_t end   = __pa(vaddr + numpages * PAGE_SIZE);
> +	const int max_retries_per_page = 3;
> +	struct tdx_hypercall_args args;
> +	u64 map_fail_paddr, ret;
> +	int retry_count = 0;
>  
>  	if (!enc) {
>  		/* Set the shared (decrypted) bits: */
> @@ -718,12 +720,49 @@ static bool tdx_enc_status_changed(unsigned long vaddr, int numpages, bool enc)
>  		end   |= cc_mkdec(0);
>  	}
>  
> -	/*
> -	 * Notify the VMM about page mapping conversion. More info about ABI
> -	 * can be found in TDX Guest-Host-Communication Interface (GHCI),
> -	 * section "TDG.VP.VMCALL<MapGPA>"
> -	 */
> -	if (_tdx_hypercall(TDVMCALL_MAP_GPA, start, end - start, 0, 0))
> +	while (retry_count < max_retries_per_page) {
> +		memset(&args, 0, sizeof(args));
> +		args.r10 = TDX_HYPERCALL_STANDARD;
> +		args.r11 = TDVMCALL_MAP_GPA;
> +		args.r12 = start;
> +		args.r13 = end - start;
> +

What's wrong with:

	while (retry_count < max_retries_per_page) {
		struct tdx_hypercall_args args = {
			.r10 = TDX_HYPERCALL_STANDARD,
			.r11 = TDVMCALL_MAP_GPA,
			.r12 = start,
			.r13 = end - start };

?

Or maybe with the brackets slightly differently arranged.

Why'd you declare all the variables outside the while() loop anyway?