linux-kernel - [PATCH v6 11/17] s390/mm: KVM: pv: when tearing down, try to destroy protected pages

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Message-Id: <20211203165814.73016-12-imbrenda@linux.ibm.com>
Date:   Fri,  3 Dec 2021 17:58:08 +0100
From:   Claudio Imbrenda <imbrenda@...ux.ibm.com>
To:     kvm@...r.kernel.org
Cc:     cohuck@...hat.com, borntraeger@...ibm.com, frankja@...ux.ibm.com,
        thuth@...hat.com, pasic@...ux.ibm.com, david@...hat.com,
        linux-s390@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH v6 11/17] s390/mm: KVM: pv: when tearing down, try to destroy protected pages

When ptep_get_and_clear_full is called for a mm teardown, we will now
attempt to destroy the secure pages. This will be faster than export.

In case it was not a teardown, or if for some reason the destroy page
UVC failed, we try with an export page, like before.

Signed-off-by: Claudio Imbrenda <imbrenda@...ux.ibm.com>
---
 arch/s390/include/asm/pgtable.h | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/arch/s390/include/asm/pgtable.h b/arch/s390/include/asm/pgtable.h
index 23ca0d8e058a..c008b354573e 100644
--- a/arch/s390/include/asm/pgtable.h
+++ b/arch/s390/include/asm/pgtable.h
@@ -1118,9 +1118,14 @@ static inline pte_t ptep_get_and_clear_full(struct mm_struct *mm,
 	} else {
 		res = ptep_xchg_lazy(mm, addr, ptep, __pte(_PAGE_INVALID));
 	}
+	/* Nothing to do */
+	if (!mm_is_protected(mm) || !pte_present(res))
+		return res;
 	/* At this point the reference through the mapping is still present */
-	if (mm_is_protected(mm) && pte_present(res))
-		uv_convert_owned_from_secure(pte_val(res) & PAGE_MASK);
+	if (full && !uv_destroy_owned_page(pte_val(res) & PAGE_MASK))
+		return res;
+	/* If could not destroy, we try export */
+	uv_convert_owned_from_secure(pte_val(res) & PAGE_MASK);
 	return res;
 }
 
-- 
2.31.1