linux-kernel - Re: [RFC, PATCH 02/12] x86/virt/tdx: Allocate reference counters for PAMT memory

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Message-ID: <aB3QUKanj5KajTs9@intel.com>
Date: Fri, 9 May 2025 17:52:16 +0800
From: Chao Gao <chao.gao@...el.com>
To: "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
CC: <pbonzini@...hat.com>, <seanjc@...gle.com>, <rick.p.edgecombe@...el.com>,
	<isaku.yamahata@...el.com>, <kai.huang@...el.com>, <yan.y.zhao@...el.com>,
	<tglx@...utronix.de>, <mingo@...hat.com>, <bp@...en8.de>,
	<dave.hansen@...ux.intel.com>, <kvm@...r.kernel.org>, <x86@...nel.org>,
	<linux-coco@...ts.linux.dev>, <linux-kernel@...r.kernel.org>
Subject: Re: [RFC, PATCH 02/12] x86/virt/tdx: Allocate reference counters for
 PAMT memory

>+static int init_pamt_metadata(void)
>+{
>+	size_t size = max_pfn / PTRS_PER_PTE * sizeof(*pamt_refcounts);
>+	struct vm_struct *area;
>+
>+	if (!tdx_supports_dynamic_pamt(&tdx_sysinfo))
>+		return 0;
>+
>+	/*
>+	 * Reserve vmalloc range for PAMT reference counters. It covers all
>+	 * physical address space up to max_pfn. It is going to be populated
>+	 * from init_tdmr() only for present memory that available for TDX use.
>+	 */
>+	area = get_vm_area(size, VM_IOREMAP);
>+	if (!area)
>+		return -ENOMEM;
>+
>+	pamt_refcounts = area->addr;
>+	return 0;
>+}
>+
>+static void free_pamt_metadata(void)
>+{
>+	size_t size = max_pfn / PTRS_PER_PTE * sizeof(*pamt_refcounts);
>+

Shouldn't the free path also be gated by tdx_supports_dynamic_pamt()?

There is a possibility that pamt_refcounts could be NULL here, e.g., the
TDX module doesn't support dynamic PAMT and init_tdmrs() encountered an
error.  I am assuming that apply_to_existing_page_range() below will cause
issues if pamt_refcounts is NULL, e.g., unmap mappings set up by others.

>+	size = round_up(size, PAGE_SIZE);
>+	apply_to_existing_page_range(&init_mm,
>+				     (unsigned long)pamt_refcounts,
>+				     size, pamt_refcount_depopulate,
>+				     NULL);
>+	vfree(pamt_refcounts);
>+	pamt_refcounts = NULL;
>+}
>+
> static int init_tdmr(struct tdmr_info *tdmr)
> {
> 	u64 next;
>+	int ret;
>+
>+	ret = alloc_tdmr_pamt_refcount(tdmr);
>+	if (ret)
>+		return ret;
> 
> 	/*
> 	 * Initializing a TDMR can be time consuming.  To avoid long
>@@ -1048,7 +1150,6 @@ static int init_tdmr(struct tdmr_info *tdmr)
> 		struct tdx_module_args args = {
> 			.rcx = tdmr->base,
> 		};
>-		int ret;
> 
> 		ret = seamcall_prerr_ret(TDH_SYS_TDMR_INIT, &args);
> 		if (ret)
>@@ -1134,10 +1235,15 @@ static int init_tdx_module(void)
> 	if (ret)
> 		goto err_reset_pamts;
> 
>+	/* Reserve vmalloc range for PAMT reference counters */
>+	ret = init_pamt_metadata();
>+	if (ret)
>+		goto err_reset_pamts;
>+
> 	/* Initialize TDMRs to complete the TDX module initialization */
> 	ret = init_tdmrs(&tdx_tdmr_list);
> 	if (ret)
>-		goto err_reset_pamts;
>+		goto err_free_pamt_metadata;
> 
> 	pr_info("%lu KB allocated for PAMT\n", tdmrs_count_pamt_kb(&tdx_tdmr_list));
> 
>@@ -1149,6 +1255,9 @@ static int init_tdx_module(void)
> 	put_online_mems();
> 	return ret;
> 
>+err_free_pamt_metadata:
>+	free_pamt_metadata();
>+
> err_reset_pamts:
> 	/*
> 	 * Part of PAMTs may already have been initialized by the
>-- 
>2.47.2
>