linux-kernel - [PATCH v2 08/10] kvm: arm64: Mark hyp stack pages reserved

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Message-Id: <20200903091712.46456-9-dbrazdil@google.com>
Date:   Thu,  3 Sep 2020 11:17:10 +0200
From:   David Brazdil <dbrazdil@...gle.com>
To:     Marc Zyngier <maz@...nel.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>, Dennis Zhou <dennis@...nel.org>,
        Tejun Heo <tj@...nel.org>, Christoph Lameter <cl@...ux.com>,
        Arnd Bergmann <arnd@...db.de>
Cc:     James Morse <james.morse@....com>,
        Julien Thierry <julien.thierry.kdev@...il.com>,
        Suzuki K Poulose <suzuki.poulose@....com>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        kvmarm@...ts.cs.columbia.edu, linux-arch@...r.kernel.org,
        kernel-team@...roid.com, David Brazdil <dbrazdil@...gle.com>
Subject: [PATCH v2 08/10] kvm: arm64: Mark hyp stack pages reserved

In preparation for unmapping hyp pages from host stage-2, allocate/free hyp
stack using new helpers which automatically mark the pages reserved.

Signed-off-by: David Brazdil <dbrazdil@...gle.com>
---
 arch/arm64/kvm/arm.c | 49 ++++++++++++++++++++++++++++++++++++++++++--
 1 file changed, 47 insertions(+), 2 deletions(-)

diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c
index d437052c5481..8a1fcf4dffca 100644
--- a/arch/arm64/kvm/arm.c
+++ b/arch/arm64/kvm/arm.c
@@ -1453,13 +1453,58 @@ static int init_subsystems(void)
 	return err;
 }
 
+/*
+ * Alloc pages and mark them reserved so the kernel never tries to
+ * take them away from the hypervisor.
+ */
+static unsigned long alloc_hyp_pages(gfp_t flags, unsigned int order)
+{
+	struct page *page;
+	unsigned long i;
+
+	page = alloc_pages(flags, order);
+	if (!page)
+		return 0;
+
+	for (i = 0; i < (1ul << order); ++i)
+		mark_page_reserved(page + i);
+
+	return (unsigned long)page_address(page);
+}
+
+static unsigned long alloc_hyp_page(gfp_t flags)
+{
+	return alloc_hyp_pages(flags, 0);
+}
+
+/*
+ * Free pages which were previously marked reserved for the hypervisor.
+ */
+static void free_hyp_pages(unsigned long addr, unsigned int order)
+{
+	unsigned long i;
+	struct page *page;
+
+	if (!addr)
+		return;
+
+	page = virt_to_page(addr);
+	for (i = 0; i < (1ul << order); ++i)
+		free_reserved_page(page + i);
+}
+
+static void free_hyp_page(unsigned long addr)
+{
+	return free_hyp_pages(addr, 0);
+}
+
 static void teardown_hyp_mode(void)
 {
 	int cpu;
 
 	free_hyp_pgds();
 	for_each_possible_cpu(cpu)
-		free_page(per_cpu(kvm_arm_hyp_stack_page, cpu));
+		free_hyp_page(per_cpu(kvm_arm_hyp_stack_page, cpu));
 }
 
 /**
@@ -1483,7 +1528,7 @@ static int init_hyp_mode(void)
 	for_each_possible_cpu(cpu) {
 		unsigned long stack_page;
 
-		stack_page = __get_free_page(GFP_KERNEL);
+		stack_page = alloc_hyp_page(GFP_KERNEL);
 		if (!stack_page) {
 			err = -ENOMEM;
 			goto out_err;
-- 
2.28.0.402.g5ffc5be6b7-goog