linux-kernel - Re: [PATCH v12 17/29] KVM: SEV: Add support to handle RMP nested page faults

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Date: Sat, 30 Mar 2024 21:55:37 +0100
From: Paolo Bonzini <pbonzini@...hat.com>
To: Michael Roth <michael.roth@....com>, kvm@...r.kernel.org
Cc: linux-coco@...ts.linux.dev, linux-mm@...ck.org,
 linux-crypto@...r.kernel.org, x86@...nel.org, linux-kernel@...r.kernel.org,
 tglx@...utronix.de, mingo@...hat.com, jroedel@...e.de,
 thomas.lendacky@....com, hpa@...or.com, ardb@...nel.org, seanjc@...gle.com,
 vkuznets@...hat.com, jmattson@...gle.com, luto@...nel.org,
 dave.hansen@...ux.intel.com, slp@...hat.com, pgonda@...gle.com,
 peterz@...radead.org, srinivas.pandruvada@...ux.intel.com,
 rientjes@...gle.com, dovmurik@...ux.ibm.com, tobin@....com, bp@...en8.de,
 vbabka@...e.cz, kirill@...temov.name, ak@...ux.intel.com,
 tony.luck@...el.com, sathyanarayanan.kuppuswamy@...ux.intel.com,
 alpergun@...gle.com, jarkko@...nel.org, ashish.kalra@....com,
 nikunj.dadhania@....com, pankaj.gupta@....com, liam.merwick@...cle.com,
 Brijesh Singh <brijesh.singh@....com>
Subject: Re: [PATCH v12 17/29] KVM: SEV: Add support to handle RMP nested page
 faults

On 3/29/24 23:58, Michael Roth wrote:
> +	if (rmp_level == PG_LEVEL_4K) {
> +		pr_debug_ratelimited("%s: Spurious RMP fault for GPA 0x%llx, error_code 0x%llx",
> +				     __func__, gpa, error_code);
> +		goto out;
> +	}
> +
> +	pr_debug_ratelimited("%s: Splitting 2M RMP entry for GPA 0x%llx, error_code 0x%llx",
> +			     __func__, gpa, error_code);
> +	ret = snp_rmptable_psmash(pfn);
> +	if (ret && ret != PSMASH_FAIL_INUSE) {
> +		/*
> +		 * Look it up again. If it's 4K now then the PSMASH may have raced with
> +		 * another process and the issue has already resolved itself.
> +		 */
> +		if (!snp_lookup_rmpentry(pfn, &assigned, &rmp_level) && assigned &&
> +		    rmp_level == PG_LEVEL_4K) {
> +			pr_debug_ratelimited("%s: PSMASH for GPA 0x%llx failed with ret %d due to potential race",
> +					     __func__, gpa, ret);
> +			goto out;
> +		}

Please change these pr_debug_ratelimited() to just a single trace point 
after the call to snp_rmptable_psmash().

Paolo