linux-kernel - [RFC PATCH v7 15/16] xpfo, mm: Fix hang when booting with "xpfotlbflush"

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Date:   Thu, 10 Jan 2019 14:09:47 -0700
From:   Khalid Aziz <khalid.aziz@...cle.com>
To:     juergh@...il.com, tycho@...ho.ws, jsteckli@...zon.de,
        ak@...ux.intel.com, torvalds@...ux-foundation.org,
        liran.alon@...cle.com, keescook@...gle.com, konrad.wilk@...cle.com
Cc:     Khalid Aziz <khalid.aziz@...cle.com>, deepa.srinivasan@...cle.com,
        chris.hyser@...cle.com, tyhicks@...onical.com, dwmw@...zon.co.uk,
        andrew.cooper3@...rix.com, jcm@...hat.com,
        boris.ostrovsky@...cle.com, kanth.ghatraju@...cle.com,
        joao.m.martins@...cle.com, jmattson@...gle.com,
        pradeep.vincent@...cle.com, john.haxby@...cle.com,
        tglx@...utronix.de, kirill.shutemov@...ux.intel.com, hch@....de,
        steven.sistare@...cle.com, kernel-hardening@...ts.openwall.com,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: [RFC PATCH v7 15/16] xpfo, mm: Fix hang when booting with "xpfotlbflush"

Kernel hangs when booted up with "xpfotlbflush" option. This is caused
by xpfo_kunmap() fliushing TLB while holding xpfo lock starving other
tasks waiting for the lock. This patch moves tlb flush outside of the
code holding xpfo lock.

Signed-off-by: Khalid Aziz <khalid.aziz@...cle.com>
---
 mm/xpfo.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/mm/xpfo.c b/mm/xpfo.c
index 85079377c91d..79ffdba6af69 100644
--- a/mm/xpfo.c
+++ b/mm/xpfo.c
@@ -148,6 +148,8 @@ EXPORT_SYMBOL(xpfo_kmap);
 
 void xpfo_kunmap(void *kaddr, struct page *page)
 {
+	bool flush_tlb = false;
+
 	if (!static_branch_unlikely(&xpfo_inited))
 		return;
 
@@ -168,10 +170,13 @@ void xpfo_kunmap(void *kaddr, struct page *page)
 		if (atomic_read(&page->xpfo_mapcount) == 0) {
 			SetPageXpfoUnmapped(page);
 			set_kpte(kaddr, page, __pgprot(0));
-			xpfo_cond_flush_kernel_tlb(page, 0);
+			flush_tlb = true;
 		}
 		spin_unlock(&page->xpfo_lock);
 	}
+
+	if (flush_tlb)
+		xpfo_cond_flush_kernel_tlb(page, 0);
 }
 EXPORT_SYMBOL(xpfo_kunmap);
 
-- 
2.17.1