Message-ID: <a15fc9a5-c136-47f7-e15e-776a511f3cdb@intel.com>
Date:   Wed, 1 Mar 2023 08:21:17 -0800
MIME-Version: 1.0
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101
 Thunderbird/102.7.1
Subject: Re: [PATCH RFC v8 17/56] x86/fault: Add support to handle the RMP
 fault for user address
Content-Language: en-US
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,
        rientjes@google.com, dovmurik@linux.ibm.com, tobin@ibm.com,
        bp@alien8.de, vbabka@suse.cz, 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>,
        Jarkko Sakkinen <jarkko.sakkinen@profian.com>
References: <20230220183847.59159-1-michael.roth@amd.com>
 <20230220183847.59159-18-michael.roth@amd.com>
From:   Dave Hansen <dave.hansen@intel.com>
In-Reply-To: <20230220183847.59159-18-michael.roth@amd.com>
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 7bit
Precedence: bulk

On 2/20/23 10:38, Michael Roth wrote:
> +static int handle_split_page_fault(struct vm_fault *vmf)
> +{
> +	__split_huge_pmd(vmf->vma, vmf->pmd, vmf->address, false, NULL);
> +	return 0;
> +}
> +
>  /*
>   * By the time we get here, we already hold the mm semaphore
>   *
> @@ -5078,6 +5084,10 @@ static vm_fault_t __handle_mm_fault(struct vm_area_struct *vma,
>  				pmd_migration_entry_wait(mm, vmf.pmd);
>  			return 0;
>  		}
> +
> +		if (flags & FAULT_FLAG_PAGE_SPLIT)
> +			return handle_split_page_fault(&vmf);

I asked this long ago, but how do you prevent these faults from
occurring on hugetlbfs mappings that can't be split?