[PATCH v6 05/18] KVM: arm64: Allow kvm_hyp_memcache usage outside of stage-2

[Vincent Donnefort <vdonnefort@google.com>]

Although currently limited to guest stage-2 page-table allocations,
struct kvm_hyp_memcache is a useful primitive for passing a list of
discontiguous pages between host and hypervisor.

Introduce init_hyp_memcache() to initialise a generic hyp memcache, and
init_hyp_stage2_memcache() for stage-2 specific memcaches. The generic
initialiser will be used to top up the upcoming pKVM heap allocator.

Note that the generic kvm_hyp_memcache does not account for the
allocated memory. This is expected: donations to the heap allocator are
shared and recycled, they cannot be accounted for a specific VM.

Signed-off-by: Vincent Donnefort <vdonnefort@google.com>
Reviewed-by: Fuad Tabba <fuad.tabba@linux.dev>
Tested-by: Fuad Tabba <fuad.tabba@linux.dev>
---
 arch/arm64/include/asm/kvm_host.h | 13 +++++++++++++
 arch/arm64/kvm/mmu.c              |  4 +++-
 arch/arm64/kvm/pkvm.c             |  4 ++--
 3 files changed, 18 insertions(+), 3 deletions(-)

diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
index fc1a82777ed4..64cd6233b439 100644
--- a/arch/arm64/include/asm/kvm_host.h
+++ b/arch/arm64/include/asm/kvm_host.h
@@ -92,9 +92,22 @@ struct kvm_hyp_memcache {
 	struct pkvm_mapping *mapping; /* only used from EL1 */
 
 #define	HYP_MEMCACHE_ACCOUNT_STAGE2	BIT(1)
+#define	HYP_MEMCACHE_ACCOUNT_KMEMCG	BIT(2)
 	unsigned long flags;
 };
 
+static inline void init_hyp_memcache(struct kvm_hyp_memcache *mc)
+{
+	memset(mc, 0, sizeof(*mc));
+	mc->mapping = ZERO_SIZE_PTR; /* Prevent allocation, solely useful for stage2 memcache */
+}
+
+static inline void init_hyp_stage2_memcache(struct kvm_hyp_memcache *mc)
+{
+	memset(mc, 0, sizeof(*mc));
+	mc->flags = HYP_MEMCACHE_ACCOUNT_STAGE2 | HYP_MEMCACHE_ACCOUNT_KMEMCG;
+}
+
 static inline void push_hyp_memcache(struct kvm_hyp_memcache *mc,
 				     phys_addr_t *p,
 				     phys_addr_t (*to_pa)(void *virt))
diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c
index 9ba86450fe4a..3163502cc7d2 100644
--- a/arch/arm64/kvm/mmu.c
+++ b/arch/arm64/kvm/mmu.c
@@ -1160,8 +1160,10 @@ static void *hyp_mc_alloc_fn(void *mc)
 {
 	struct kvm_hyp_memcache *memcache = mc;
 	void *addr;
+	gfp_t gfp;
 
-	addr = (void *)__get_free_page(GFP_KERNEL_ACCOUNT);
+	gfp = memcache->flags & HYP_MEMCACHE_ACCOUNT_KMEMCG ? GFP_KERNEL_ACCOUNT : GFP_KERNEL;
+	addr = (void *)__get_free_page(gfp);
 	if (addr && memcache->flags & HYP_MEMCACHE_ACCOUNT_STAGE2)
 		kvm_account_pgtable_pages(addr, 1);
 
diff --git a/arch/arm64/kvm/pkvm.c b/arch/arm64/kvm/pkvm.c
index 8e4c6e4bec12..e5200731a45b 100644
--- a/arch/arm64/kvm/pkvm.c
+++ b/arch/arm64/kvm/pkvm.c
@@ -111,7 +111,7 @@ static int __pkvm_create_hyp_vcpu(struct kvm_vcpu *vcpu)
 	void *hyp_vcpu;
 	int ret;
 
-	vcpu->arch.pkvm_memcache.flags |= HYP_MEMCACHE_ACCOUNT_STAGE2;
+	init_hyp_stage2_memcache(&vcpu->arch.pkvm_memcache);
 
 	hyp_vcpu = alloc_pages_exact(hyp_vcpu_sz, GFP_KERNEL_ACCOUNT);
 	if (!hyp_vcpu)
@@ -172,7 +172,7 @@ static int __pkvm_create_hyp_vm(struct kvm *kvm)
 		goto free_vm;
 
 	kvm->arch.pkvm.is_created = true;
-	kvm->arch.pkvm.stage2_teardown_mc.flags |= HYP_MEMCACHE_ACCOUNT_STAGE2;
+	init_hyp_stage2_memcache(&kvm->arch.pkvm.stage2_teardown_mc);
 	kvm_account_pgtable_pages(pgd, pgd_sz / PAGE_SIZE);
 
 	return 0;
-- 
2.56.0.rc1.315.gc6ed9934b7-goog