On Wed, Dec 09, 2020 at 01:54:42PM +0100, Borislav Petkov wrote: > On Wed, Dec 09, 2020 at 12:29:07PM +0000, Ashish Kalra wrote: > > As i mentioned in the main comments above, this cannot be called in > > mem_encrypt_init() as that breaks reserve_crashkernel() which depends > > on SWIOTLB buffer size > > Please elaborate how does it break. >
reserve_crashkernel() calls swiotlb_size_or_default() to get SWIOTLB buffer size and then accordingly allocates low memory for crashkernel. If SWIOTLB buffer size is adjusted after reserve_crashkernel() and swiotlb_size_or_default(), then SWIOTLB buffers will overlap the memory reserved for crashkernel. Hence any SWIOTLB buffer adjustment needs to be done before or in swiotlb_size_or_default(), but Konrad is not in favor of modifying swiotlb_size_or_default(), hence this separate swiotlb_adjust() interface is introduced. > > and is called before mem_encrypt_init(), therefore, it needs to be > > called from setup_atch() before reserve_crashkernel(). > > I know you have your requirements what needs to be called when like all > the other vendors who want to run stuff early in a particular order but > our boot init order is a single fragile mess. So this better be done > right! > > Also, > > [ 0.016630] software IO TLB: swiotlb_adjust: > [ 0.017005] reserve_crashkernel: > [ 0.050523] software IO TLB: swiotlb_init: > > this looks strange - we're doing a swiotlb size adjust before init. > > It probably makes sense as in: adjust the size before the SWIOTLB is > initialized so that it uses the correct size but this better be spelled > out. > Yes the adjustment is done before init. > > I believe that other memory encryption architectures such as s390 are > > also looking for something similar to be available. > > Until you have something more palpable than belief, "let the others > extend it when they really need it." as I already mentioned. There is a need to introduce an architecture specific callback for swiotlb_adjust() because of the following reason : The sev_active() function is only available to x86, so this will break other archs, if we use this function in generic swiotlb code. Therefore, we need arch-specific callback/interface to be invoked from generic swiotlb code to do the SEV specific actions such as SWIOTLB buffer size adjustment. Thanks, Ashish
