linux-kernel - Re: [PATCHv2 04/12] x86/virt/tdx: Add tdx_alloc/free

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Message-ID: <aEeaJH1KqZ38tgKi@intel.com>
Date: Tue, 10 Jun 2025 10:36:20 +0800
From: Chao Gao <chao.gao@...el.com>
To: "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
CC: <pbonzini@...hat.com>, <seanjc@...gle.com>, <dave.hansen@...ux.intel.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>, <kvm@...r.kernel.org>, <x86@...nel.org>,
	<linux-coco@...ts.linux.dev>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCHv2 04/12] x86/virt/tdx: Add tdx_alloc/free_page() helpers

>+static int tdx_alloc_pamt_pages(struct list_head *pamt_pages)
>+{
>+	for (int i = 0; i < tdx_nr_pamt_pages(); i++) {
>+		struct page *page = alloc_page(GFP_KERNEL);
>+		if (!page)
>+			goto fail;

this goto isn't needed. it is used only once. so we can just free the pages and
return -ENOMEM here.

>+		list_add(&page->lru, pamt_pages);
>+	}
>+	return 0;
>+fail:
>+	tdx_free_pamt_pages(pamt_pages);
>+	return -ENOMEM;
>+}
>+
>+static int tdx_pamt_add(atomic_t *pamt_refcount, unsigned long hpa,
>+			struct list_head *pamt_pages)
>+{
>+	u64 err;
>+
>+	guard(spinlock)(&pamt_lock);
>+
>+	hpa = ALIGN_DOWN(hpa, PMD_SIZE);
>+
>+	/* Lost race to other tdx_pamt_add() */
>+	if (atomic_read(pamt_refcount) != 0) {
>+		atomic_inc(pamt_refcount);
>+		return 1;
>+	}
>+
>+	err = tdh_phymem_pamt_add(hpa | TDX_PS_2M, pamt_pages);
>+
>+	/*
>+	 * tdx_hpa_range_not_free() is true if current task won race
>+	 * against tdx_pamt_put().
>+	 */
>+	if (err && !tdx_hpa_range_not_free(err)) {
>+		pr_err("TDH_PHYMEM_PAMT_ADD failed: %#llx\n", err);
>+		return -EIO;
>+	}
>+
>+	atomic_set(pamt_refcount, 1);
>+
>+	if (tdx_hpa_range_not_free(err))
>+		return 1;

I think this needs a comment for the return values 0/1/-EIO above the function.

>+
>+	return 0;
>+}
>+
>+static int tdx_pamt_get(struct page *page, enum pg_level level)
>+{
>+	unsigned long hpa = page_to_phys(page);
>+	atomic_t *pamt_refcount;
>+	LIST_HEAD(pamt_pages);
>+	int ret;
>+
>+	if (!tdx_supports_dynamic_pamt(&tdx_sysinfo))
>+		return 0;
>+
>+	if (level != PG_LEVEL_4K)
>+		return 0;

This also needs a comment. i.e., why return success directly for large pages?

<snip>