From: Sathyanarayanan Kuppuswamy <sathyanarayanan.kuppuswamy@linux.intel.com>
To: Kai Huang <kai.huang@intel.com>,
"Kirill A. Shutemov" <kirill@shutemov.name>
Cc: Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
Dave Hansen <dave.hansen@linux.intel.com>,
x86@kernel.org, "H . Peter Anvin" <hpa@zytor.com>,
"Kirill A . Shutemov" <kirill.shutemov@linux.intel.com>,
Tony Luck <tony.luck@intel.com>, Andi Kleen <ak@linux.intel.com>,
Wander Lairson Costa <wander@redhat.com>,
Isaku Yamahata <isaku.yamahata@gmail.com>,
marcelo.cerri@canonical.com, tim.gardner@canonical.com,
khalid.elmously@canonical.com, philip.cox@canonical.com,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH v5 3/3] x86/tdx: Add Quote generation support
Date: Mon, 2 May 2022 19:39:04 -0700 [thread overview]
Message-ID: <ac299f99-7ef6-7fc2-a9fe-7ed2586b9b09@linux.intel.com> (raw)
In-Reply-To: <4cf22a0799cc13fa6f09ffbf0e5d83ed7eeb32ad.camel@intel.com>
On 5/2/22 7:18 PM, Kai Huang wrote:
> On Tue, 2022-05-03 at 04:27 +0300, Kirill A. Shutemov wrote:
>> On Mon, May 02, 2022 at 02:40:26PM +1200, Kai Huang wrote:
>>>
>>>> +
>>>> + /* Get order for Quote buffer page allocation */
>>>> + order = get_order(quote_req.len);
>>>> +
>>>> + /*
>>>> + * Allocate buffer to get TD Quote from the VMM.
>>>> + * Size needs to be 4KB aligned (which is already
>>>> + * met in page allocation).
>>>> + */
>>>> + tdquote = (void *)__get_free_pages(GFP_KERNEL | __GFP_ZERO, order);
>>>> + if (!tdquote) {
>>>> + ret = -ENOMEM;
>>>> + goto quote_failed;
>>>> + }
>>>
>>> You can use alloc_pages_exact().
>>>
>>>> +
>>>> + /*
>>>> + * Since this buffer will be shared with the VMM via GetQuote
>>>> + * hypercall, decrypt it.
>>>> + */
>>>> + ret = set_memory_decrypted((unsigned long)tdquote, 1UL << order);
>>>> + if (ret)
>>>> + goto quote_failed;
>>>
>>>
>>> Again, Dave and Andi already commented you should use vmap() to avoid breaking
>>> up the direct-mapping. Please use vmap() instead.
>>>
>>> https://lore.kernel.org/all/ce0feeec-a949-35f8-3010-b0d69acbbc2e@linux.intel.com/
>>>
>>> Will review the rest later.
>>
>> I would rather convert it to use DMA API for memory allocation. It will
>> tap into swiotlb buffer that already converted and there's no need to
>> touch direct mapping. Both allocation and freeing such memory is cheaper
>> because of that.
>>
>
> Does each DMA allocation and free internally do the actual private/shared
> conversion? Or the swiotlb is converted at the beginning at boot and DMA
> allocation will always get the shared buffer automatically?
DMA allocation will always return shared buffer.
>
> The problem of using DMA API is it will need to bring additional code to use
> platform device, which isn't necessary.
Yes.
>
> Using vmap() we can still (almost) avoid private/shared conversion at IOCTL time
> by allocating a default size buffer (which is large enough to cover 99% cases,
> etc) at driver initialization time:
Allocating fixed size buffer pool will work for dma buffer allocation
as well.
So the comparison is between platform driver boilerplate code vs vmap
and shared/unshared code addition. It is arguable which is better. I
think it is about preference.
>
> https://lore.kernel.org/lkml/20220422233418.1203092-2-sathyanarayanan.kuppuswamy@linux.intel.com/T/#maf7e5f6894548972c5de71f607199a79645856ff
>
>
--
Sathyanarayanan Kuppuswamy
Linux Kernel Developer
next prev parent reply other threads:[~2022-05-03 2:39 UTC|newest]
Thread overview: 56+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-05-01 18:34 [PATCH v5 0/3] Add TDX Guest Attestation support Kuppuswamy Sathyanarayanan
2022-05-01 18:34 ` [PATCH v5 1/3] x86/tdx: Add TDX Guest attestation interface driver Kuppuswamy Sathyanarayanan
2022-05-02 2:31 ` Kai Huang
2022-05-02 15:52 ` Sathyanarayanan Kuppuswamy
2022-05-02 22:30 ` Kai Huang
2022-05-02 23:17 ` Sathyanarayanan Kuppuswamy
2022-05-02 23:37 ` Kai Huang
2022-05-03 14:38 ` Wander Costa
2022-05-03 15:09 ` Sathyanarayanan Kuppuswamy
2022-05-03 22:08 ` Kai Huang
2022-05-02 12:18 ` Wander Lairson Costa
2022-05-02 16:06 ` Sathyanarayanan Kuppuswamy
2022-05-01 18:34 ` [PATCH v5 2/3] x86/tdx: Add TDX Guest event notify interrupt support Kuppuswamy Sathyanarayanan
2022-05-02 12:44 ` Wander Lairson Costa
2022-05-01 18:35 ` [PATCH v5 3/3] x86/tdx: Add Quote generation support Kuppuswamy Sathyanarayanan
2022-05-02 2:40 ` Kai Huang
2022-05-03 1:27 ` Kirill A. Shutemov
2022-05-03 2:18 ` Kai Huang
2022-05-03 2:39 ` Sathyanarayanan Kuppuswamy [this message]
2022-05-03 22:13 ` Kai Huang
2022-05-03 2:45 ` Kirill A. Shutemov
2022-05-03 3:36 ` Kai Huang
2022-05-03 22:24 ` Dave Hansen
2022-05-03 22:28 ` Sathyanarayanan Kuppuswamy
2022-05-03 22:30 ` Sathyanarayanan Kuppuswamy
2022-05-04 22:49 ` Sathyanarayanan Kuppuswamy
2022-05-04 23:28 ` Kai Huang
2022-05-05 20:53 ` Sathyanarayanan Kuppuswamy
2022-05-05 22:15 ` Kai Huang
2022-05-05 22:38 ` Sathyanarayanan Kuppuswamy
2022-05-05 23:06 ` Dave Hansen
2022-05-06 0:11 ` Kai Huang
2022-05-06 1:55 ` Sathyanarayanan Kuppuswamy
2022-05-07 0:42 ` Kirill A. Shutemov
2022-05-09 3:37 ` Kai Huang
2022-05-09 12:09 ` Kirill A. Shutemov
2022-05-09 14:14 ` Dave Hansen
2022-05-09 15:35 ` Kirill A. Shutemov
2022-05-09 15:43 ` Sathyanarayanan Kuppuswamy
2022-05-09 23:54 ` Kai Huang
2022-05-10 0:17 ` Sathyanarayanan Kuppuswamy
2022-05-10 1:30 ` Kirill A. Shutemov
2022-05-10 1:40 ` Kai Huang
2022-05-10 10:42 ` Kai Huang
2022-05-16 17:39 ` Sathyanarayanan Kuppuswamy
2022-05-06 11:00 ` Kai Huang
2022-05-06 15:47 ` Dave Hansen
2022-05-07 1:00 ` Kirill A. Shutemov
2022-05-05 10:50 ` Kai Huang
2022-05-05 19:03 ` Sathyanarayanan Kuppuswamy
2022-05-05 22:25 ` Kai Huang
2022-05-02 5:01 ` Kai Huang
2022-05-02 16:02 ` Sathyanarayanan Kuppuswamy
2022-05-02 23:02 ` Kai Huang
2022-05-02 13:16 ` Wander Lairson Costa
2022-05-02 16:05 ` Sathyanarayanan Kuppuswamy
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