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Subject: Re: [PATCH Part2 v5 08/45] x86/fault: Add support to handle the RMP
 fault for user address
To:     Dave Hansen <dave.hansen@intel.com>, x86@kernel.org,
        linux-kernel@vger.kernel.org, kvm@vger.kernel.org,
        linux-coco@lists.linux.dev, linux-mm@kvack.org,
        linux-crypto@vger.kernel.org
References: <20210820155918.7518-1-brijesh.singh@amd.com>
 <20210820155918.7518-9-brijesh.singh@amd.com>
 <f6d778a0-840d-8c9c-392d-5c9ffcc0bdc6@intel.com>
From:   Brijesh Singh <brijesh.singh@amd.com>
Message-ID: <19599ede-9fc5-25e1-dcb3-98aafd8b7e87@amd.com>
Date:   Mon, 23 Aug 2021 09:36:05 -0500
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Hi Dave,

On 8/23/21 9:20 AM, Dave Hansen wrote:
> On 8/20/21 8:58 AM, Brijesh Singh wrote:
>> +static int handle_split_page_fault(struct vm_fault *vmf)
>> +{
>> +	if (!IS_ENABLED(CONFIG_AMD_MEM_ENCRYPT))
>> +		return VM_FAULT_SIGBUS;
>> +
>> +	__split_huge_pmd(vmf->vma, vmf->pmd, vmf->address, false, NULL);
>> +	return 0;
>> +}
> 
> We had a whole conversation the last time this was posted about huge
> page types *other* than THP.  I don't see any comprehension of those
> types or what would happen if one of those was used with SEV-SNP.
> 
> What was the result of those review comments?
> 

Based on previous review comments Sean was not keen on KVM having 
perform this detection and abort the guest SEV-SNP VM launch. So, I 
didn't implemented the check and waiting for more discussion before 
going at it.

SEV-SNP guest requires the VMM to register the guest backing pages 
before the VM launch. Personally, I would prefer KVM to check the 
backing page type during the registration and fail to register if its 
hugetlbfs (and others) to avoid us get into situation where we could not 
split the hugepage.

thanks

> I'm still worried that hugetlbfs (and others) are not properly handled
> by this series.
>