linux-kernel - Re: [PATCH v11 42/45] virt: Add SEV-SNP guest driver

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Message-ID: <9c075b36-e450-831b-0ae2-3b680686beb4@amd.com>
Date:   Fri, 4 Mar 2022 07:17:33 -0600
From:   Brijesh Singh <brijesh.singh@....com>
To:     Dave Hansen <dave.hansen@...el.com>, x86@...nel.org,
        linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        linux-efi@...r.kernel.org, platform-driver-x86@...r.kernel.org,
        linux-coco@...ts.linux.dev, linux-mm@...ck.org
Cc:     brijesh.singh@....com, Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Joerg Roedel <jroedel@...e.de>,
        Tom Lendacky <thomas.lendacky@....com>,
        "H. Peter Anvin" <hpa@...or.com>, Ard Biesheuvel <ardb@...nel.org>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Jim Mattson <jmattson@...gle.com>,
        Andy Lutomirski <luto@...nel.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Sergio Lopez <slp@...hat.com>, Peter Gonda <pgonda@...gle.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>,
        David Rientjes <rientjes@...gle.com>,
        Dov Murik <dovmurik@...ux.ibm.com>,
        Tobin Feldman-Fitzthum <tobin@....com>,
        Borislav Petkov <bp@...en8.de>,
        Michael Roth <michael.roth@....com>,
        Vlastimil Babka <vbabka@...e.cz>,
        "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
        Andi Kleen <ak@...ux.intel.com>,
        "Dr . David Alan Gilbert" <dgilbert@...hat.com>,
        brijesh.ksingh@...il.com, tony.luck@...el.com, marcorr@...gle.com,
        sathyanarayanan.kuppuswamy@...ux.intel.com
Subject: Re: [PATCH v11 42/45] virt: Add SEV-SNP guest driver


On 3/3/22 11:33 AM, Dave Hansen wrote:

...


>> +	 */
>> +	if (count >= UINT_MAX) {
>> +		pr_err_ratelimited("request message sequence counter overflow\n");
>> +		return 0;
>> +	}
>> +
>> +	return count;
>> +}
> I didn't see a pr_fmt defined anywhere.  But, for a "driver", should
> this be a dev_err()?


Okay, I can switch to dev_err() and will define pr_fmt.

> ...
>> +static void free_shared_pages(void *buf, size_t sz)
>> +{
>> +	unsigned int npages = PAGE_ALIGN(sz) >> PAGE_SHIFT;
>> +
>> +	if (!buf)
>> +		return;
>> +
>> +	if (WARN_ONCE(set_memory_encrypted((unsigned long)buf, npages),
>> +		      "failed to restore encryption mask (leak it)\n"))
>> +		return;
>> +
>> +	__free_pages(virt_to_page(buf), get_order(sz));
>> +}
> Nit: It's a bad practice to do important things inside a WARN_ON() _or_
> and if().  This should be:
>
> 	int ret;
>
> 	...
>
> 	ret = set_memory_encrypted((unsigned long)buf, npages));
>
> 	if (ret) {
> 		WARN_ONCE(...);
> 		return;
> 	}
> 	
> BTW, this look like a generic allocator thingy.  But it's only ever used
> to allocate a 'struct snp_guest_msg'.  Why all the trouble to allocate
> and free one fixed-size structure?  The changelog and comments don't
> shed any light.

The GHCB specification says that a guest must use shared memory for
request, response, and certificate blob. In this patch, you are seeing
that {alloc,free}_shared_pages() used only to alloc/free the request and
response page. In the last patch, we used the same generic function to
allocate the certificate blob with a different size (~16K) than 'struct
snp_guest_msg.'


thanks