linux-kernel - Re: [PATCH 3/5] crypto: ccp: Play nice with vmalloc'd memory for SEV command structs

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Message-ID: <YGsnjqFLoqXTrAHo@google.com>
Date:   Mon, 5 Apr 2021 15:06:54 +0000
From:   Sean Christopherson <seanjc@...gle.com>
To:     Christophe Leroy <christophe.leroy@...roup.eu>
Cc:     Paolo Bonzini <pbonzini@...hat.com>,
        Brijesh Singh <brijesh.singh@....com>,
        Tom Lendacky <thomas.lendacky@....com>,
        John Allen <john.allen@....com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>, kvm@...r.kernel.org,
        linux-crypto@...r.kernel.org, linux-kernel@...r.kernel.org,
        Borislav Petkov <bp@...e.de>
Subject: Re: [PATCH 3/5] crypto: ccp: Play nice with vmalloc'd memory for SEV
 command structs

On Sun, Apr 04, 2021, Christophe Leroy wrote:
> 
> Le 03/04/2021 à 01:37, Sean Christopherson a écrit :
> > @@ -152,11 +153,21 @@ static int __sev_do_cmd_locked(int cmd, void *data, int *psp_ret)
> >   	sev = psp->sev_data;
> >   	buf_len = sev_cmd_buffer_len(cmd);
> > -	if (WARN_ON_ONCE(!!data != !!buf_len))
> > +	if (WARN_ON_ONCE(!!__data != !!buf_len))
> >   		return -EINVAL;
> > -	if (WARN_ON_ONCE(data && is_vmalloc_addr(data)))
> > -		return -EINVAL;
> > +	if (__data && is_vmalloc_addr(__data)) {
> > +		/*
> > +		 * If the incoming buffer is virtually allocated, copy it to
> > +		 * the driver's scratch buffer as __pa() will not work for such
> > +		 * addresses, vmalloc_to_page() is not guaranteed to succeed,
> > +		 * and vmalloc'd data may not be physically contiguous.
> > +		 */
> > +		data = sev->cmd_buf;
> > +		memcpy(data, __data, buf_len);
> > +	} else {
> > +		data = __data;
> > +	}
> 
> I don't know how big commands are, but if they are small, it would probably
> be more efficient to inconditionnally copy them to the buffer rather then
> doing the test.

Brijesh, I assume SNP support will need to copy the commands unconditionally? If
yes, it probably makes sense to do so now and avoid vmalloc dependencies
completely.  And I think that would allow for the removal of status_cmd_buf and
init_cmd_buf, or is there another reason those dedicated buffers exist?