linux-kernel - [PATCH] KVM: SEV: Pin SEV guest memory out of CMA area

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Message-Id: <1736498887-28180-1-git-send-email-yangge1116@126.com>
Date: Fri, 10 Jan 2025 16:48:07 +0800
From: yangge1116@....com
To: pbonzini@...hat.com
Cc: kvm@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	michael.roth@....com,
	21cnbao@...il.com,
	david@...hat.com,
	baolin.wang@...ux.alibaba.com,
	liuzixing@...on.cn,
	yangge <yangge1116@....com>
Subject: [PATCH] KVM: SEV: Pin SEV guest memory out of CMA area

From: yangge <yangge1116@....com>

When pin_user_pages_fast() pins SEV guest memory without the
FOLL_LONGTERM flag, the pinned pages may inadvertently end up in the
CMA (Contiguous Memory Allocator) area. This can subsequently cause
cma_alloc() to fail in allocating these pages, due to the fact that
the pinned pages are not migratable.

To address the aforementioned problem, we propose adding the
FOLL_LONGTERM flag to the pin_user_pages_fast() function. By doing
so, we ensure that the pages allocated will not occupy space within
the CMA area, thereby preventing potential allocation failures.

Signed-off-by: yangge <yangge1116@....com>
---
 arch/x86/kvm/svm/sev.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c
index 943bd07..35d0714 100644
--- a/arch/x86/kvm/svm/sev.c
+++ b/arch/x86/kvm/svm/sev.c
@@ -630,6 +630,7 @@ static struct page **sev_pin_memory(struct kvm *kvm, unsigned long uaddr,
 	unsigned long locked, lock_limit;
 	struct page **pages;
 	unsigned long first, last;
+	unsigned int flags = 0;
 	int ret;
 
 	lockdep_assert_held(&kvm->lock);
@@ -662,8 +663,10 @@ static struct page **sev_pin_memory(struct kvm *kvm, unsigned long uaddr,
 	if (!pages)
 		return ERR_PTR(-ENOMEM);
 
+	flags = write ? FOLL_WRITE : 0;
+
 	/* Pin the user virtual address. */
-	npinned = pin_user_pages_fast(uaddr, npages, write ? FOLL_WRITE : 0, pages);
+	npinned = pin_user_pages_fast(uaddr, npages, flags | FOLL_LONGTERM, pages);
 	if (npinned != npages) {
 		pr_err("SEV: Failure locking %lu pages.\n", npages);
 		ret = -ENOMEM;
-- 
2.7.4