linux-kernel - Re: [PATCH Part1 v5 17/38] x86/mm: Add support to validate memory when changing C-bit

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Date:   Wed, 25 Aug 2021 08:54:31 -0500
From:   Brijesh Singh <brijesh.singh@....com>
To:     Borislav Petkov <bp@...en8.de>
Cc:     brijesh.singh@....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,
        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>,
        Wanpeng Li <wanpengli@...cent.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>,
        Michael Roth <michael.roth@....com>,
        Vlastimil Babka <vbabka@...e.cz>,
        "Kirill A . Shutemov" <kirill@...temov.name>,
        Andi Kleen <ak@...ux.intel.com>, tony.luck@...el.com,
        marcorr@...gle.com, sathyanarayanan.kuppuswamy@...ux.intel.com
Subject: Re: [PATCH Part1 v5 17/38] x86/mm: Add support to validate memory
 when changing C-bit



On 8/25/21 6:06 AM, Borislav Petkov wrote:
> 
> I really meant putting the beginning of that string at the very first
> position on the line:
> 
>                  if (WARN(hdr->end_entry > end_entry || cur_entry > hdr->cur_entry,
> "SEV-SNP: PSC processing going backward, end_entry %d (got %d) cur_entry %d (got %d)\n",
>                           end_entry, hdr->end_entry, cur_entry, hdr->cur_entry)) {
> 
> Exactly like this!
> 

Noted.

> ...
> 
>> +static void set_page_state(unsigned long vaddr, unsigned int npages, int op)
>> +{
>> +	unsigned long vaddr_end, next_vaddr;
>> +	struct snp_psc_desc *desc;
>> +
>> +	vaddr = vaddr & PAGE_MASK;
>> +	vaddr_end = vaddr + (npages << PAGE_SHIFT);
>> +
>> +	desc = kmalloc(sizeof(*desc), GFP_KERNEL_ACCOUNT);
> 
> And again, from previous review:
> 
> kzalloc() so that you don't have to memset() later in
> __set_page_state().
> 

I replied to your previous comment. Depending on the npages value, the 
__set_page_state() will be called multiple times and on each call it 
needs to clear desc before populate it. So, I do not see strong reason 
to use kzalloc() during the desc allocation. I thought you were okay 
with that explanation.


>> +	if (!desc)
>> +		panic("SEV-SNP: failed to alloc memory for PSC descriptor\n");
> 
> "allocate" fits just fine too.
> 

Noted.

thanks