linux-kernel - [PATCH v12 10/18] s390/mm: KVM: pv: when tearing down, try to destroy protected pages

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Message-Id: <20220628135619.32410-11-imbrenda@linux.ibm.com>
Date:   Tue, 28 Jun 2022 15:56:11 +0200
From:   Claudio Imbrenda <imbrenda@...ux.ibm.com>
To:     kvm@...r.kernel.org
Cc:     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, scgl@...ux.ibm.com,
        mimu@...ux.ibm.com, nrb@...ux.ibm.com
Subject: [PATCH v12 10/18] 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>
Acked-by: Janosch Frank <frankja@...ux.ibm.com>
Reviewed-by: Nico Boehr <nrb@...ux.ibm.com>
---
 arch/s390/include/asm/pgtable.h | 19 ++++++++++++++++---
 1 file changed, 16 insertions(+), 3 deletions(-)

diff --git a/arch/s390/include/asm/pgtable.h b/arch/s390/include/asm/pgtable.h
index f16403ba81ec..cf81acf3879c 100644
--- a/arch/s390/include/asm/pgtable.h
+++ b/arch/s390/include/asm/pgtable.h
@@ -1182,9 +1182,22 @@ static inline pte_t ptep_get_and_clear_full(struct mm_struct *mm,
 	} else {
 		res = ptep_xchg_lazy(mm, addr, ptep, __pte(_PAGE_INVALID));
 	}
-	/* 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);
+	/* Nothing to do */
+	if (!mm_is_protected(mm) || !pte_present(res))
+		return res;
+	/*
+	 * At this point the reference through the mapping is still present.
+	 * The notifier should have destroyed all protected vCPUs at this
+	 * point, so the destroy should be successful.
+	 */
+	if (full && !uv_destroy_owned_page(pte_val(res) & PAGE_MASK))
+		return res;
+	/*
+	 * If something went wrong and the page could not be destroyed, or
+	 * if this is not a mm teardown, the slower export is used as
+	 * fallback instead.
+	 */
+	uv_convert_owned_from_secure(pte_val(res) & PAGE_MASK);
 	return res;
 }
 
-- 
2.36.1