linux-kernel - [PATCH 2/2] KVM: SVM: convert get_user_pages() --> pin_user

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Date:   Mon, 25 May 2020 23:22:07 -0700
From:   John Hubbard <jhubbard@...dia.com>
To:     LKML <linux-kernel@...r.kernel.org>
CC:     Souptick Joarder <jrdr.linux@...il.com>,
        John Hubbard <jhubbard@...dia.com>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Thomas Gleixner <tglx@...utronix.de>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>,
        "H . Peter Anvin" <hpa@...or.com>, <x86@...nel.org>,
        <kvm@...r.kernel.org>
Subject: [PATCH 2/2] KVM: SVM: convert get_user_pages() --> pin_user_pages()

This code was using get_user_pages*(), in a "Case 2" scenario
(DMA/RDMA), using the categorization from [1]. That means that it's
time to convert the get_user_pages*() + put_page() calls to
pin_user_pages*() + unpin_user_pages() calls.

There is some helpful background in [2]: basically, this is a small
part of fixing a long-standing disconnect between pinning pages, and
file systems' use of those pages.

[1] Documentation/core-api/pin_user_pages.rst

[2] "Explicit pinning of user-space pages":
    https://lwn.net/Articles/807108/

Cc: Ingo Molnar <mingo@...hat.com>
Cc: Borislav Petkov <bp@...en8.de>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: Paolo Bonzini <pbonzini@...hat.com>
Cc: Sean Christopherson <sean.j.christopherson@...el.com>
Cc: Vitaly Kuznetsov <vkuznets@...hat.com>
Cc: Wanpeng Li <wanpengli@...cent.com>
Cc: Jim Mattson <jmattson@...gle.com>
Cc: Joerg Roedel <joro@...tes.org>
Cc: H. Peter Anvin <hpa@...or.com>
Cc: x86@...nel.org
Cc: kvm@...r.kernel.org
Signed-off-by: John Hubbard <jhubbard@...dia.com>
---
 arch/x86/kvm/svm/sev.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c
index 9693db1af57c..a83f2e73bcbb 100644
--- a/arch/x86/kvm/svm/sev.c
+++ b/arch/x86/kvm/svm/sev.c
@@ -349,7 +349,7 @@ static struct page **sev_pin_memory(struct kvm *kvm, unsigned long uaddr,
 		return NULL;
 
 	/* Pin the user virtual address. */
-	npinned = get_user_pages_fast(uaddr, npages, write ? FOLL_WRITE : 0, pages);
+	npinned = pin_user_pages_fast(uaddr, npages, write ? FOLL_WRITE : 0, pages);
 	if (npinned != npages) {
 		pr_err("SEV: Failure locking %lu pages.\n", npages);
 		goto err;
@@ -362,7 +362,7 @@ static struct page **sev_pin_memory(struct kvm *kvm, unsigned long uaddr,
 
 err:
 	if (npinned > 0)
-		release_pages(pages, npinned);
+		unpin_user_pages(pages, npinned);
 
 	kvfree(pages);
 	return NULL;
@@ -373,7 +373,7 @@ static void sev_unpin_memory(struct kvm *kvm, struct page **pages,
 {
 	struct kvm_sev_info *sev = &to_kvm_svm(kvm)->sev_info;
 
-	release_pages(pages, npages);
+	unpin_user_pages(pages, npages);
 	kvfree(pages);
 	sev->pages_locked -= npages;
 }
-- 
2.26.2