KVM: arm/arm64: Limit icache invalidation to prefetch aborts

We've so far eagerly invalidated the icache, no matter how
the page was faulted in (data or prefetch abort).

But we can easily track execution by setting the XN bits
in the S2 page tables, get the prefetch abort at HYP and
perform the icache invalidation at that time only.

As for most VMs, the instruction working set is pretty
small compared to the data set, this is likely to save
some traffic (specially as the invalidation is broadcast).

Reviewed-by: Christoffer Dall <christoffer.dall@linaro.org>
Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
Signed-off-by: Christoffer Dall <christoffer.dall@linaro.org>

diff --git a/arch/arm/include/asm/kvm_mmu.h b/arch/arm/include/asm/kvm_mmu.h
index bc8d21e..4d7a54c 100644 (file)
--- a/arch/arm/include/asm/kvm_mmu.h
+++ b/arch/arm/include/asm/kvm_mmu.h
@@ -85,6 +85,18 @@ static inline pmd_t kvm_s2pmd_mkwrite(pmd_t pmd)
        return pmd;
 }
 
+static inline pte_t kvm_s2pte_mkexec(pte_t pte)
+{
+       pte_val(pte) &= ~L_PTE_XN;
+       return pte;
+}
+
+static inline pmd_t kvm_s2pmd_mkexec(pmd_t pmd)
+{
+       pmd_val(pmd) &= ~PMD_SECT_XN;
+       return pmd;
+}
+
 static inline void kvm_set_s2pte_readonly(pte_t *pte)
 {
        pte_val(*pte) = (pte_val(*pte) & ~L_PTE_S2_RDWR) | L_PTE_S2_RDONLY;

diff --git a/arch/arm/include/asm/pgtable.h b/arch/arm/include/asm/pgtable.h
index 150ece6..a757401 100644 (file)
--- a/arch/arm/include/asm/pgtable.h
+++ b/arch/arm/include/asm/pgtable.h
@@ -102,8 +102,8 @@ extern pgprot_t             pgprot_s2_device;
 #define PAGE_HYP_EXEC          _MOD_PROT(pgprot_kernel, L_PTE_HYP | L_PTE_RDONLY)
 #define PAGE_HYP_RO            _MOD_PROT(pgprot_kernel, L_PTE_HYP | L_PTE_RDONLY | L_PTE_XN)
 #define PAGE_HYP_DEVICE                _MOD_PROT(pgprot_hyp_device, L_PTE_HYP)
-#define PAGE_S2                        _MOD_PROT(pgprot_s2, L_PTE_S2_RDONLY)
-#define PAGE_S2_DEVICE         _MOD_PROT(pgprot_s2_device, L_PTE_S2_RDONLY)
+#define PAGE_S2                        _MOD_PROT(pgprot_s2, L_PTE_S2_RDONLY | L_PTE_XN)
+#define PAGE_S2_DEVICE         _MOD_PROT(pgprot_s2_device, L_PTE_S2_RDONLY | L_PTE_XN)
 
 #define __PAGE_NONE            __pgprot(_L_PTE_DEFAULT | L_PTE_RDONLY | L_PTE_XN | L_PTE_NONE)
 #define __PAGE_SHARED          __pgprot(_L_PTE_DEFAULT | L_PTE_USER | L_PTE_XN)

diff --git a/arch/arm64/include/asm/kvm_mmu.h b/arch/arm64/include/asm/kvm_mmu.h
index 56b3e03..1e1b20c 100644 (file)
--- a/arch/arm64/include/asm/kvm_mmu.h
+++ b/arch/arm64/include/asm/kvm_mmu.h
@@ -173,6 +173,18 @@ static inline pmd_t kvm_s2pmd_mkwrite(pmd_t pmd)
        return pmd;
 }
 
+static inline pte_t kvm_s2pte_mkexec(pte_t pte)
+{
+       pte_val(pte) &= ~PTE_S2_XN;
+       return pte;
+}
+
+static inline pmd_t kvm_s2pmd_mkexec(pmd_t pmd)
+{
+       pmd_val(pmd) &= ~PMD_S2_XN;
+       return pmd;
+}
+
 static inline void kvm_set_s2pte_readonly(pte_t *pte)
 {
        pteval_t old_pteval, pteval;

diff --git a/arch/arm64/include/asm/pgtable-prot.h b/arch/arm64/include/asm/pgtable-prot.h
index 0a5635f..4e12dab 100644 (file)
--- a/arch/arm64/include/asm/pgtable-prot.h
+++ b/arch/arm64/include/asm/pgtable-prot.h
@@ -60,8 +60,8 @@
 #define PAGE_HYP_RO            __pgprot(_PAGE_DEFAULT | PTE_HYP | PTE_RDONLY | PTE_HYP_XN)
 #define PAGE_HYP_DEVICE                __pgprot(PROT_DEVICE_nGnRE | PTE_HYP)
 
-#define PAGE_S2                        __pgprot(PROT_DEFAULT | PTE_S2_MEMATTR(MT_S2_NORMAL) | PTE_S2_RDONLY)
-#define PAGE_S2_DEVICE         __pgprot(PROT_DEFAULT | PTE_S2_MEMATTR(MT_S2_DEVICE_nGnRE) | PTE_S2_RDONLY | PTE_UXN)
+#define PAGE_S2                        __pgprot(PROT_DEFAULT | PTE_S2_MEMATTR(MT_S2_NORMAL) | PTE_S2_RDONLY | PTE_S2_XN)
+#define PAGE_S2_DEVICE         __pgprot(PROT_DEFAULT | PTE_S2_MEMATTR(MT_S2_DEVICE_nGnRE) | PTE_S2_RDONLY | PTE_S2_XN)
 
 #define PAGE_NONE              __pgprot(((_PAGE_DEFAULT) & ~PTE_VALID) | PTE_PROT_NONE | PTE_RDONLY | PTE_PXN | PTE_UXN)
 #define PAGE_SHARED            __pgprot(_PAGE_DEFAULT | PTE_USER | PTE_NG | PTE_PXN | PTE_UXN | PTE_WRITE)

diff --git a/virt/kvm/arm/mmu.c b/virt/kvm/arm/mmu.c
index 2174244..0417c8e 100644 (file)
--- a/virt/kvm/arm/mmu.c
+++ b/virt/kvm/arm/mmu.c
@@ -1292,7 +1292,7 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
                          unsigned long fault_status)
 {
        int ret;
-       bool write_fault, writable, hugetlb = false, force_pte = false;
+       bool write_fault, exec_fault, writable, hugetlb = false, force_pte = false;
        unsigned long mmu_seq;
        gfn_t gfn = fault_ipa >> PAGE_SHIFT;
        struct kvm *kvm = vcpu->kvm;
@@ -1304,7 +1304,10 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
        unsigned long flags = 0;
 
        write_fault = kvm_is_write_fault(vcpu);
-       if (fault_status == FSC_PERM && !write_fault) {
+       exec_fault = kvm_vcpu_trap_is_iabt(vcpu);
+       VM_BUG_ON(write_fault && exec_fault);
+
+       if (fault_status == FSC_PERM && !write_fault && !exec_fault) {
                kvm_err("Unexpected L2 read permission error\n");
                return -EFAULT;
        }
@@ -1398,7 +1401,11 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
                        kvm_set_pfn_dirty(pfn);
                }
                clean_dcache_guest_page(vcpu, pfn, PMD_SIZE);
-               invalidate_icache_guest_page(vcpu, pfn, PMD_SIZE);
+
+               if (exec_fault) {
+                       new_pmd = kvm_s2pmd_mkexec(new_pmd);
+                       invalidate_icache_guest_page(vcpu, pfn, PMD_SIZE);
+               }
 
                ret = stage2_set_pmd_huge(kvm, memcache, fault_ipa, &new_pmd);
        } else {
@@ -1410,7 +1417,11 @@ static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
                        mark_page_dirty(kvm, gfn);
                }
                clean_dcache_guest_page(vcpu, pfn, PAGE_SIZE);
-               invalidate_icache_guest_page(vcpu, pfn, PAGE_SIZE);
+
+               if (exec_fault) {
+                       new_pte = kvm_s2pte_mkexec(new_pte);
+                       invalidate_icache_guest_page(vcpu, pfn, PAGE_SIZE);
+               }
 
                ret = stage2_set_pte(kvm, memcache, fault_ipa, &new_pte, flags);
        }