Re: [RFC Part2 PATCH v3 16/26] KVM: SVM: Add support for SEV LAUNCH_UPDATE_DATA command

[Brijesh Singh]

On 09/13/2017 12:55 PM, Borislav Petkov wrote:
...

> > +
> > +	/* pin the user virtual address */
> > +	pinned = get_user_pages_fast(uaddr, npages, write ? FOLL_WRITE : 0,
> > +					pages);
>
> Let it stick out.


Will do.

...


> > +	vaddr = params.address;
> > +	size = params.length;
> > +	vaddr_end = vaddr + size;
> > +
> > +	/* lock the user memory */
> > +	inpages = sev_pin_memory(vaddr, size, &npages, 1);
>
> This way user basically controls how many pages to pin and you need to
> limit that on the upper end.

Actually I don't know what should be sane upper bound in this case --
typically we encrypt the guest BIOS using LAUNCH_UPDATE_DATA command.
I have heard that some user may want to create a pre-encrypted image
(which may contains guest BIOS + kernel + initrd) -- this can be huge.

For SEV guest, we have been needing to pin the memory hence how about if
we limit the number of pages to pin with rlimit ? The rlimit check can
also include the guest RAM pinning.


> > +	if (!inpages) {
> > +		ret = -ENOMEM;
> > +		goto e_free;
> > +	}
> > +
> > +	/*
> > +	 * invalidate the cache to ensure that DRAM has recent content before
>
> recent content?


Cache access from the PSP are coherent with x86 but not other way around --
I will update the comments to reflect the true meaning.

...

> Yah, let it stick out.

Okay.