Messages in this thread | | | Subject | Re: AMD SME encrpytion and PCI BAR pages to user space | From | Tom Lendacky <> | Date | Mon, 19 Oct 2020 11:36:16 -0500 |
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On 10/19/20 10:25 AM, Jason Gunthorpe wrote: > Hi Tom,
Hi Jason,
> > We've found a bug where systems that have the AMD SME turned on are > not able to run RDMA work loads. It seems the kernel is automatically > encrypting VMA's pointing at PCI BAR memory created by > io_remap_pfn_range() - adding a prot_decrypted() causes things to > start working. > > To me this is surprising, before I go adding random prot_decrypted() > into the RDMA subsystem can you confirm this is actually how things > are expected to work?
Yes, currently, the idea is that anything being done in user space is mapped encrypted.
> > Is RDMA missing something? I don't see anything special in VFIO for > instance and the two are very similar - does VFIO work with SME, eg > DPDK or something unrelated to virtualization?
If user space is mapping un-encrypted memory, then, yes, it would seem that there is a gap in the support where the pgprot_decrypted() would be needed in order to override the protection map.
> > Is there a reason not to just add prot_decrypted() to > io_remap_pfn_range()? Is there use cases where a caller actually wants > encrypted io memory?
As long as you never have physical memory / ram being mapped in this path, it seems that applying pgprot_decrypted() would be ok.
> > I saw your original patch series edited a few drivers this way, but > not nearly enough. So I feel like I'm missing something.. Does vfio > work with SME? I couldn't find any sign of it calling prot_decrypted() > either?
I haven't tested SME with VFIO/DPDK.
> > (BTW, I don't have any AMD SME systems to test on here, I'm getting > this bug report from deployed system, running a distro kernel)
As a work around, if the system has support for TSME (transparent SME), then that can be enabled (it is a BIOS option that the BIOS vendor would have had to expose) to encrypt all of the system memory without requiring SME support.
Thanks, Tom
> > Thanks, > Jason >
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