linux-kernel - Re: [PATCH v11 11/20] x86/virt/tdx: Fill out TDMRs to cover all TDX memory regions

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Message-ID: <20230612143355.sur7zc7byu7omxal@box.shutemov.name>
Date:   Mon, 12 Jun 2023 17:33:55 +0300
From:   "kirill.shutemov@...ux.intel.com" <kirill.shutemov@...ux.intel.com>
To:     "Huang, Kai" <kai.huang@...el.com>
Cc:     "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "Hansen, Dave" <dave.hansen@...el.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "Luck, Tony" <tony.luck@...el.com>,
        "david@...hat.com" <david@...hat.com>,
        "bagasdotme@...il.com" <bagasdotme@...il.com>,
        "ak@...ux.intel.com" <ak@...ux.intel.com>,
        "Wysocki, Rafael J" <rafael.j.wysocki@...el.com>,
        "Chatre, Reinette" <reinette.chatre@...el.com>,
        "Christopherson,, Sean" <seanjc@...gle.com>,
        "pbonzini@...hat.com" <pbonzini@...hat.com>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "Yamahata, Isaku" <isaku.yamahata@...el.com>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "Shahar, Sagi" <sagis@...gle.com>,
        "peterz@...radead.org" <peterz@...radead.org>,
        "imammedo@...hat.com" <imammedo@...hat.com>,
        "Gao, Chao" <chao.gao@...el.com>,
        "Brown, Len" <len.brown@...el.com>,
        "sathyanarayanan.kuppuswamy@...ux.intel.com" 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>,
        "Huang, Ying" <ying.huang@...el.com>,
        "Williams, Dan J" <dan.j.williams@...el.com>
Subject: Re: [PATCH v11 11/20] x86/virt/tdx: Fill out TDMRs to cover all TDX
 memory regions

On Mon, Jun 12, 2023 at 02:33:58AM +0000, Huang, Kai wrote:
> 
> > 
> > Maybe not even a pr_warn(), but something that's a bit ominous and has a
> > chance of getting users to act.
> 
> Sorry I am not sure how to do.  Could you give some suggestion?

Maybe something like this would do?

I'm struggle with the warning message. Any suggestion is welcome.

diff --git a/arch/x86/virt/vmx/tdx/tdx.c b/arch/x86/virt/vmx/tdx/tdx.c
index 9cd4f6b58d4a..cc141025b249 100644
--- a/arch/x86/virt/vmx/tdx/tdx.c
+++ b/arch/x86/virt/vmx/tdx/tdx.c
@@ -627,6 +627,15 @@ static int fill_out_tdmrs(struct list_head *tmb_list,
 	/* @tdmr_idx is always the index of last valid TDMR. */
 	tdmr_list->nr_consumed_tdmrs = tdmr_idx + 1;
 
+	/*
+	 * Warn early that kernel is about to run out of TDMRs.
+	 *
+	 * This is indication that TDMR allocation has to be reworked to be
+	 * smarter to not run into an issue.
+	 */
+	if (tdmr_list->max_tdmrs - tdmr_list->nr_consumed_tdmrs < TDMR_NR_WARN)
+		pr_warn("Low number of spare TDMRs\n");
+
 	return 0;
 }
 
diff --git a/arch/x86/virt/vmx/tdx/tdx.h b/arch/x86/virt/vmx/tdx/tdx.h
index 323ce744b853..17efe33847ae 100644
--- a/arch/x86/virt/vmx/tdx/tdx.h
+++ b/arch/x86/virt/vmx/tdx/tdx.h
@@ -98,6 +98,9 @@ struct tdx_memblock {
 	int nid;
 };
 
+/* Warn if kernel has less than TDMR_NR_WARN TDMRs after allocation */
+#define TDMR_NR_WARN 4
+
 struct tdmr_info_list {
 	void *tdmrs;	/* Flexible array to hold 'tdmr_info's */
 	int nr_consumed_tdmrs;	/* How many 'tdmr_info's are in use */
-- 
  Kiryl Shutsemau / Kirill A. Shutemov