linux-kernel - Re: [PATCH v12 08/22] x86/virt/tdx: Get information about TDX module and TDX-capable memory

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Message-ID: <20230627095124.nhiypr6ivi4kdfrw@box.shutemov.name>
Date:   Tue, 27 Jun 2023 12:51:24 +0300
From:   kirill.shutemov@...ux.intel.com
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,
        tony.luck@...el.com, peterz@...radead.org, 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 08/22] x86/virt/tdx: Get information about TDX module
 and TDX-capable memory

On Tue, Jun 27, 2023 at 02:12:38AM +1200, Kai Huang wrote:
>  static int init_tdx_module(void)
>  {
> +	struct tdsysinfo_struct *sysinfo;
> +	struct cmr_info *cmr_array;
> +	int ret;
> +
> +	/*
> +	 * Get the TDSYSINFO_STRUCT and CMRs from the TDX module.
> +	 *
> +	 * The buffers of the TDSYSINFO_STRUCT and the CMR array passed
> +	 * to the TDX module must be 1024-bytes and 512-bytes aligned
> +	 * respectively.  Allocate one page to accommodate them both and
> +	 * also meet those alignment requirements.
> +	 */
> +	sysinfo = (struct tdsysinfo_struct *)__get_free_page(GFP_KERNEL);
> +	if (!sysinfo)
> +		return -ENOMEM;
> +	cmr_array = (struct cmr_info *)((unsigned long)sysinfo + PAGE_SIZE / 2);
> +
> +	BUILD_BUG_ON(PAGE_SIZE / 2 < TDSYSINFO_STRUCT_SIZE);
> +	BUILD_BUG_ON(PAGE_SIZE / 2 < sizeof(struct cmr_info) * MAX_CMRS);

This works, but why not just use slab for this? kmalloc has 512 and 1024
pools already and you won't waste memory for rounding up.

Something like this:

        sysinfo = kmalloc(TDSYSINFO_STRUCT_SIZE, GFP_KERNEL);
        if (!sysinfo)
                return -ENOMEM;

        cmr_array_size = sizeof(struct cmr_info) * MAX_CMRS;

        /* CMR array has to be 512-aligned */
        cmr_array_size = round_up(cmr_array_size, 512);

        cmr_array = kmalloc(cmr_array_size, GFP_KERNEL);
        if (!cmr_array) {
                kfree(sysinfo);
                return -ENOMEM;
        }

?

-- 
  Kiryl Shutsemau / Kirill A. Shutemov