Re: [PATCH RFC v8 12/56] x86/sev: Add RMP entry lookup helpers

[Vlastimil Babka]

On 2/20/23 19:38, Michael Roth wrote:
> From: Brijesh Singh <brijesh.singh@xxxxxxx>
> 
> The snp_lookup_page_in_rmptable() can be used by the host to read the RMP
> entry for a given page. The RMP entry format is documented in AMD PPR, see
> https://bugzilla.kernel.org/attachment.cgi?id=296015.
> 
> Co-developed-by: Ashish Kalra <ashish.kalra@xxxxxxx>
> Signed-off-by: Ashish Kalra <ashish.kalra@xxxxxxx>
> Signed-off-by: Brijesh Singh <brijesh.singh@xxxxxxx>
> Signed-off-by: Michael Roth <michael.roth@xxxxxxx>
> ---

> +/*
> + * Return 1 if the RMP entry is assigned, 0 if it exists but is not assigned,
> + * and -errno if there is no corresponding RMP entry.
> + */

Hmm IMHO the kernel's idiomatic way is to return 0 on "success" and I'd
assume the more intuitive expectation of success here if the entry is
assigned? The various callers seem to differ though so I guess it depends on
context. Some however don't distinguish their "failure" from an ERR and
maybe they should, at least for the purposes of the various printks?

> +int snp_lookup_rmpentry(u64 pfn, int *level)
> +{
> +	struct rmpentry *e;
> +
> +	e = __snp_lookup_rmpentry(pfn, level);
> +	if (IS_ERR(e))
> +		return PTR_ERR(e);
> +
> +	return !!rmpentry_assigned(e);
> +}
> +EXPORT_SYMBOL_GPL(snp_lookup_rmpentry);