Message-ID: <b48ad925-eff0-8421-730a-6da13bf93ab6@suse.cz>
Date:   Fri, 3 Mar 2023 16:28:39 +0100
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Subject: Re: [PATCH RFC v8 12/56] x86/sev: Add RMP entry lookup helpers
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To:     Michael Roth <michael.roth@amd.com>, kvm@vger.kernel.org
Cc:     linux-coco@lists.linux.dev, linux-mm@kvack.org,
        linux-crypto@vger.kernel.org, x86@kernel.org,
        linux-kernel@vger.kernel.org, tglx@linutronix.de, mingo@redhat.com,
        jroedel@suse.de, thomas.lendacky@amd.com, hpa@zytor.com,
        ardb@kernel.org, pbonzini@redhat.com, seanjc@google.com,
        vkuznets@redhat.com, jmattson@google.com, luto@kernel.org,
        dave.hansen@linux.intel.com, slp@redhat.com, pgonda@google.com,
        peterz@infradead.org, srinivas.pandruvada@linux.intel.com,
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        bp@alien8.de, kirill@shutemov.name, ak@linux.intel.com,
        tony.luck@intel.com, marcorr@google.com,
        sathyanarayanan.kuppuswamy@linux.intel.com, alpergun@google.com,
        dgilbert@redhat.com, jarkko@kernel.org, ashish.kalra@amd.com,
        nikunj.dadhania@amd.com, Brijesh Singh <brijesh.singh@amd.com>
References: <20230220183847.59159-1-michael.roth@amd.com>
 <20230220183847.59159-13-michael.roth@amd.com>
From:   Vlastimil Babka <vbabka@suse.cz>
In-Reply-To: <20230220183847.59159-13-michael.roth@amd.com>
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On 2/20/23 19:38, Michael Roth wrote:
> From: Brijesh Singh <brijesh.singh@amd.com>
> 
> 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@amd.com>
> Signed-off-by: Ashish Kalra <ashish.kalra@amd.com>
> Signed-off-by: Brijesh Singh <brijesh.singh@amd.com>
> Signed-off-by: Michael Roth <michael.roth@amd.com>
> ---

> +/*
> + * 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);