linux-kernel - Re: [RFC, PATCH 05/12] KVM: TDX: Add tdx_pamt

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Message-ID: <aCQrMh+wxDzrpAKA@intel.com>
Date: Wed, 14 May 2025 13:33:38 +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 05/12] KVM: TDX: Add tdx_pamt_get()/put() helpers

>+static void tdx_pamt_put(struct page *page)
>+{
>+	unsigned long hpa = page_to_phys(page);
>+	atomic_t *pamt_refcount;
>+	LIST_HEAD(pamt_pages);
>+	u64 err;
>+
>+	if (!tdx_supports_dynamic_pamt(tdx_sysinfo))
>+		return;
>+
>+	hpa = ALIGN_DOWN(hpa, SZ_2M);
>+
>+	pamt_refcount = tdx_get_pamt_refcount(hpa);
>+	if (!atomic_dec_and_test(pamt_refcount))
>+		return;
>+
>+	spin_lock(&pamt_lock);
>+
>+	/* Lost race against tdx_pamt_add()? */
>+	if (atomic_read(pamt_refcount) != 0) {
>+		spin_unlock(&pamt_lock);
>+		return;
>+	}
>+
>+	err = tdh_phymem_pamt_remove(hpa | TDX_PS_2M, &pamt_pages);
>+	spin_unlock(&pamt_lock);
>+
>+	if (err) {
>+		pr_tdx_error(TDH_PHYMEM_PAMT_REMOVE, err);

Should the refcount be increased here, since the PAMT pages are not removed?

>+		return;
>+	}
>+
>+	tdx_free_pamt_pages(&pamt_pages);
>+}