linux-kernel - [PATCH v2] KVM: Explicitly use GFP_KERNEL_ACCOUNT for 'struct kvm

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Message-Id: <20210406190740.4055679-1-seanjc@google.com>
Date:   Tue,  6 Apr 2021 12:07:40 -0700
From:   Sean Christopherson <seanjc@...gle.com>
To:     Paolo Bonzini <pbonzini@...hat.com>
Cc:     kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        Wanpeng Li <kernellwp@...il.com>,
        Sean Christopherson <seanjc@...gle.com>
Subject: [PATCH v2] KVM: Explicitly use GFP_KERNEL_ACCOUNT for 'struct
 kvm_vcpu' allocations

Use GFP_KERNEL_ACCOUNT when allocating vCPUs to make it more obvious that
that the allocations are accounted, to make it easier to audit KVM's
allocations in the future, and to be consistent with other cache usage in
KVM.

When using SLAB/SLUB, this is a nop as the cache itself is created with
SLAB_ACCOUNT.

When using SLOB, there are caveats within caveats.  SLOB doesn't honor
SLAB_ACCOUNT, so passing GFP_KERNEL_ACCOUNT will result in vCPU
allocations now being accounted.   But, even that depends on internal
SLOB details as SLOB will only go to the page allocator when its cache is
depleted.  That just happens to be extremely likely for vCPUs because the
size of kvm_vcpu is larger than the a page for almost all combinations of
architecture and page size.  Whether or not the SLOB behavior is by
design is unknown; it's just as likely that no SLOB users care about
accounding and so no one has bothered to implemented support in SLOB.
Regardless, accounting vCPU allocations will not break SLOB+KVM+cgroup
users, if any exist.

Cc: Wanpeng Li <kernellwp@...il.com>
Signed-off-by: Sean Christopherson <seanjc@...gle.com>
---

v2: Drop the Fixes tag and rewrite the changelog since this is a nop when
    using SLUB or SLAB. [Wanpeng]

 virt/kvm/kvm_main.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 0a481e7780f0..580f98386b42 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -3192,7 +3192,7 @@ static int kvm_vm_ioctl_create_vcpu(struct kvm *kvm, u32 id)
 	if (r)
 		goto vcpu_decrement;

-	vcpu = kmem_cache_zalloc(kvm_vcpu_cache, GFP_KERNEL);
+	vcpu = kmem_cache_zalloc(kvm_vcpu_cache, GFP_KERNEL_ACCOUNT);
 	if (!vcpu) {
 		r = -ENOMEM;
 		goto vcpu_decrement;
-- 
2.31.0.208.g409f899ff0-goog