Re: [PATCH v11 0/7] KVM: PPC: Driver to manage pages of secure guest
From: Bharata B Rao <hidden>
Date: 2019-11-28 05:04:24
Also in:
linux-mm
Subsystem:
kernel virtual machine for powerpc (kvm/powerpc), linux for powerpc (32-bit and 64-bit), the rest · Maintainers:
Madhavan Srinivasan, Michael Ellerman, Linus Torvalds
On Mon, Nov 25, 2019 at 08:36:24AM +0530, Bharata B Rao wrote:
Hi, This is the next version of the patchset that adds required support in the KVM hypervisor to run secure guests on PEF-enabled POWER platforms.
Here is a fix for the issue Hugh identified with the usage of ksm_madvise() in this patchset. It applies on top of this patchset. ---- From 8a4d769bf4c61f921c79ce68923be3c403bd5862 Mon Sep 17 00:00:00 2001 From: Bharata B Rao <redacted> Date: Thu, 28 Nov 2019 09:31:54 +0530 Subject: [PATCH 1/1] KVM: PPC: Book3S HV: Take write mmap_sem when calling ksm_madvise In order to prevent the device private pages (that correspond to pages of secure guest) from participating in KSM merging, H_SVM_PAGE_IN calls ksm_madvise() under read version of mmap_sem. However ksm_madvise() needs to be under write lock, fix this. Signed-off-by: Bharata B Rao <redacted> --- arch/powerpc/kvm/book3s_hv_uvmem.c | 29 ++++++++++++++++++++--------- 1 file changed, 20 insertions(+), 9 deletions(-)
diff --git a/arch/powerpc/kvm/book3s_hv_uvmem.c b/arch/powerpc/kvm/book3s_hv_uvmem.c
index f24ac3cfb34c..2de264fc3156 100644
--- a/arch/powerpc/kvm/book3s_hv_uvmem.c
+++ b/arch/powerpc/kvm/book3s_hv_uvmem.c@@ -46,11 +46,10 @@ * * Locking order * - * 1. srcu_read_lock(&kvm->srcu) - Protects KVM memslots - * 2. down_read(&kvm->mm->mmap_sem) - find_vma, migrate_vma_pages and helpers - * 3. mutex_lock(&kvm->arch.uvmem_lock) - protects read/writes to uvmem slots - * thus acting as sync-points - * for page-in/out + * 1. kvm->srcu - Protects KVM memslots + * 2. kvm->mm->mmap_sem - find_vma, migrate_vma_pages and helpers, ksm_madvise + * 3. kvm->arch.uvmem_lock - protects read/writes to uvmem slots thus acting + * as sync-points for page-in/out */ /*
@@ -344,7 +343,7 @@ static struct page *kvmppc_uvmem_get_page(unsigned long gpa, struct kvm *kvm) static int kvmppc_svm_page_in(struct vm_area_struct *vma, unsigned long start, unsigned long end, unsigned long gpa, struct kvm *kvm, - unsigned long page_shift) + unsigned long page_shift, bool *downgrade) { unsigned long src_pfn, dst_pfn = 0; struct migrate_vma mig;
@@ -360,8 +359,15 @@ kvmppc_svm_page_in(struct vm_area_struct *vma, unsigned long start, mig.src = &src_pfn; mig.dst = &dst_pfn; + /* + * We come here with mmap_sem write lock held just for + * ksm_madvise(), otherwise we only need read mmap_sem. + * Hence downgrade to read lock once ksm_madvise() is done. + */ ret = ksm_madvise(vma, vma->vm_start, vma->vm_end, MADV_UNMERGEABLE, &vma->vm_flags); + downgrade_write(&kvm->mm->mmap_sem); + *downgrade = true; if (ret) return ret;
@@ -456,6 +462,7 @@ unsigned long kvmppc_h_svm_page_in(struct kvm *kvm, unsigned long gpa, unsigned long flags, unsigned long page_shift) { + bool downgrade = false; unsigned long start, end; struct vm_area_struct *vma; int srcu_idx;
@@ -476,7 +483,7 @@ kvmppc_h_svm_page_in(struct kvm *kvm, unsigned long gpa, ret = H_PARAMETER; srcu_idx = srcu_read_lock(&kvm->srcu); - down_read(&kvm->mm->mmap_sem); + down_write(&kvm->mm->mmap_sem); start = gfn_to_hva(kvm, gfn); if (kvm_is_error_hva(start))
@@ -492,12 +499,16 @@ kvmppc_h_svm_page_in(struct kvm *kvm, unsigned long gpa, if (!vma || vma->vm_start > start || vma->vm_end < end) goto out_unlock; - if (!kvmppc_svm_page_in(vma, start, end, gpa, kvm, page_shift)) + if (!kvmppc_svm_page_in(vma, start, end, gpa, kvm, page_shift, + &downgrade)) ret = H_SUCCESS; out_unlock: mutex_unlock(&kvm->arch.uvmem_lock); out: - up_read(&kvm->mm->mmap_sem); + if (downgrade) + up_read(&kvm->mm->mmap_sem); + else + up_write(&kvm->mm->mmap_sem); srcu_read_unlock(&kvm->srcu, srcu_idx); return ret; }
--
2.21.0