Messages in this thread | | | Date | Mon, 2 May 2022 19:39:04 -0700 | Subject | Re: [PATCH v5 3/3] x86/tdx: Add Quote generation support | From | Sathyanarayanan Kuppuswamy <> |
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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
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