[PATCH v4 1/5] KVM: x86: Move memcache allocation to GFP_PGTABLE_USER

From: Christoffer Dall <christoffer.dall@arm.com>
To: kvm@vger.kernel.org
Cc: Wanpeng Li <wanpengli@tencent.com>,
	James Hogan <jhogan@kernel.org>, Joerg Roedel <joro@8bytes.org>,
	Anshuman Khandual <anshuman.khandual@arm.com>,
	Sean Christopherson <sean.j.christopherson@intel.com>,
	Mike Rapoport <rppt@linux.ibm.com>,
	Paul Mackerras <paulus@ozlabs.org>,
	Christian Borntraeger <borntraeger@de.ibm.com>,
	Marc Zyngier <maz@kernel.org>,
	Paolo Bonzini <pbonzini@redhat.com>,
	Vitaly Kuznetsov <vkuznets@redhat.com>,
	kvmarm@lists.cs.columbia.edu, Jim Mattson <jmattson@google.com>
Subject: [PATCH v4 1/5] KVM: x86: Move memcache allocation to GFP_PGTABLE_USER
Date: Tue,  5 Nov 2019 12:03:53 +0100	[thread overview]
Message-ID: <20191105110357.8607-2-christoffer.dall@arm.com> (raw)
In-Reply-To: <20191105110357.8607-1-christoffer.dall@arm.com>

Recent commit 50f11a8a4620eee6b6831e69ab5d42456546d7d8 moved page table
allocations for both KVM and normal user page table allocations to
GFP_PGTABLE_USER in order to get __GFP_ACCOUNT for the page tables.

However, while KVM on other architectures such as arm64 were included in
this change, curiously KVM on x86 was not.

Currently, KVM on x86 uses kmem_cache_zalloc(GFP_KERNEL_ACCOUNT) for
kmem_cache-based allocations, which expands in the following way:
  kmem_cache_zalloc(..., GFP_KERNEL_ACCOUNT) =>
  kmem_cache_alloc(..., GFP_KERNEL_ACCOUNT | __GFP_ZERO) =>
  kmem_cache_alloc(..., GFP_KERNEL | __GFP_ACCOUNT | __GFP_ZERO)

It so happens that GFP_PGTABLE_USER expands as:
  GFP_PGTABLE_USER =>
  (GFP_PGTABLE_KERNEL | __GFP_ACCOUNT) =>
  ((GFP_KERNEL | __GFP_ZERO) | __GFP_ACCOUNT) =>
  (GFP_KERNEL | __GFP_ACCOUNT | __GFP_ZERO)

Which means that we can replace the current KVM on x86 call as:
-  obj = kmem_cache_zalloc(base_cache, GFP_KERNEL_ACCOUNT);
+  obj = kmem_cache_alloc(base_cache, GFP_PGTABLE_USER);

For the single page cache topup allocation, KVM on x86 currently uses
__get_free_page(GFP_KERNEL_ACCOUNT).  It seems to me that is equivalent
to the above, except that the allocated page is not guaranteed to be
zero (unless I missed the place where __get_free_page(!__GFP_ZERO) is
still guaranteed to be zeroed.  It seems natural (and in fact desired)
to have both topup functions implement the same expectations towards the
caller, and we therefore move to GFP_PGTABLE_USER here as well.

This will make it easier to unify the memchace implementation between
architectures.

Signed-off-by: Christoffer Dall <christoffer.dall@arm.com>
---
 arch/x86/kvm/mmu.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
index 24c23c66b226..540190cee3cb 100644
--- a/arch/x86/kvm/mmu.c
+++ b/arch/x86/kvm/mmu.c
@@ -40,6 +40,7 @@
 
 #include <asm/page.h>
 #include <asm/pat.h>
+#include <asm/pgalloc.h>
 #include <asm/cmpxchg.h>
 #include <asm/e820/api.h>
 #include <asm/io.h>
@@ -1025,7 +1026,7 @@ static int mmu_topup_memory_cache(struct kvm_mmu_memory_cache *cache,
 	if (cache->nobjs >= min)
 		return 0;
 	while (cache->nobjs < ARRAY_SIZE(cache->objects)) {
-		obj = kmem_cache_zalloc(base_cache, GFP_KERNEL_ACCOUNT);
+		obj = kmem_cache_alloc(base_cache, GFP_PGTABLE_USER);
 		if (!obj)
 			return cache->nobjs >= min ? 0 : -ENOMEM;
 		cache->objects[cache->nobjs++] = obj;
@@ -1053,7 +1054,7 @@ static int mmu_topup_memory_cache_page(struct kvm_mmu_memory_cache *cache,
 	if (cache->nobjs >= min)
 		return 0;
 	while (cache->nobjs < ARRAY_SIZE(cache->objects)) {
-		page = (void *)__get_free_page(GFP_KERNEL_ACCOUNT);
+		page = (void *)__get_free_page(GFP_PGTABLE_USER);
 		if (!page)
 			return cache->nobjs >= min ? 0 : -ENOMEM;
 		cache->objects[cache->nobjs++] = page;
-- 
2.18.0

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