linux-kernel - Re: [RFC Part2 PATCH 07/30] mm: add support to split the large THP based on RMP violation

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Date:   Thu, 25 Mar 2021 07:30:37 -0700
From:   Dave Hansen <dave.hansen@...el.com>
To:     Brijesh Singh <brijesh.singh@....com>,
        linux-kernel@...r.kernel.org, x86@...nel.org, kvm@...r.kernel.org,
        linux-crypto@...r.kernel.org
Cc:     ak@...ux.intel.com, herbert@...dor.apana.org.au,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Joerg Roedel <jroedel@...e.de>,
        "H. Peter Anvin" <hpa@...or.com>, Tony Luck <tony.luck@...el.com>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Tom Lendacky <thomas.lendacky@....com>,
        David Rientjes <rientjes@...gle.com>,
        Sean Christopherson <seanjc@...gle.com>
Subject: Re: [RFC Part2 PATCH 07/30] mm: add support to split the large THP
 based on RMP violation

On 3/24/21 10:04 AM, Brijesh Singh wrote:
> @@ -1377,6 +1442,22 @@ void do_user_addr_fault(struct pt_regs *regs,
>  	if (hw_error_code & X86_PF_INSTR)
>  		flags |= FAULT_FLAG_INSTRUCTION;
>  
> +	/*
> +	 * If its an RMP violation, see if we can resolve it.
> +	 */
> +	if ((hw_error_code & X86_PF_RMP)) {
> +		ret = handle_rmp_page_fault(hw_error_code, address);
> +		if (ret == RMP_FAULT_PAGE_SPLIT) {
> +			flags |= FAULT_FLAG_PAGE_SPLIT;
> +		} else if (ret == RMP_FAULT_KILL) {
> +			fault |= VM_FAULT_SIGBUS;
> +			mm_fault_error(regs, hw_error_code, address, fault);
> +			return;
> +		} else {
> +			return;
> +		}
> +	}

Won't khugepaged come right back around and coalesce this page again?