linux-kernel - Re: [PATCH v13 01/12] swiotlb: Refactor swiotlb init functions

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Message-ID: <20210618143212.GA19284@lst.de>
Date:   Fri, 18 Jun 2021 16:32:12 +0200
From:   Christoph Hellwig <hch@....de>
To:     Tom Lendacky <thomas.lendacky@....com>
Cc:     Claire Chang <tientzu@...omium.org>,
        Stefano Stabellini <sstabellini@...nel.org>,
        Rob Herring <robh+dt@...nel.org>, mpe@...erman.id.au,
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Subject: Re: [PATCH v13 01/12] swiotlb: Refactor swiotlb init functions

On Fri, Jun 18, 2021 at 09:09:17AM -0500, Tom Lendacky wrote:
> > swiotlb_init_with_tbl uses memblock_alloc to allocate the io_tlb_mem
> > and memblock_alloc[1] will do memset in memblock_alloc_try_nid[2], so
> > swiotlb_init_with_tbl is also good.
> > I'm happy to add the memset in swiotlb_init_io_tlb_mem if you think
> > it's clearer and safer.
> 
> On x86, if the memset is done before set_memory_decrypted() and memory
> encryption is active, then the memory will look like ciphertext afterwards
> and not be zeroes. If zeroed memory is required, then a memset must be
> done after the set_memory_decrypted() calls.

Which should be fine - we don't care that the memory is cleared to 0,
just that it doesn't leak other data.  Maybe a comment would be useful,
though,