Subject: [PATCH v3 04/11] arm64: KVM: flush VM pages before letting the guest enable caches

From: [email-masked] (Christoffer Dall)
Date: Thu, 6 Feb 2014 20:08:28 -0800

On Wed, Feb 05, 2014 at 07:55:44PM +0000, Marc Zyngier wrote:
> When the guest runs with caches disabled (like in an early boot
> sequence, for example), all the writes are diectly going to RAM,
> bypassing the caches altogether.
> 
> Once the MMU and caches are enabled, whatever sits in the cache
> becomes suddenly visible, which isn't what the guest expects.
> 
> A way to avoid this potential disaster is to invalidate the cache
> when the MMU is being turned on. For this, we hook into the SCTLR_EL1
> trapping code, and scan the stage-2 page tables, invalidating the
> pages/sections that have already been mapped in.
> 
> Signed-off-by: Marc Zyngier <[email-masked]>
> Reviewed-by: Catalin Marinas <[email-masked]>
> ---
>  arch/arm/include/asm/kvm_mmu.h   |  8 ++++
>  arch/arm/kvm/mmu.c               | 93 ++++++++++++++++++++++++++++++++++++++++
>  arch/arm64/include/asm/kvm_mmu.h |  4 ++
>  arch/arm64/kvm/sys_regs.c        |  5 ++-
>  4 files changed, 109 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/arm/include/asm/kvm_mmu.h b/arch/arm/include/asm/kvm_mmu.h
> index 6d0f3d3..0931cda 100644
> --- a/arch/arm/include/asm/kvm_mmu.h
> +++ b/arch/arm/include/asm/kvm_mmu.h
> @@ -114,6 +114,12 @@ static inline void kvm_set_s2pmd_writable(pmd_t *pmd)
>  	pmd_val(*pmd) |= L_PMD_S2_RDWR;
>  }
>  
> +/* Open coded pgd_addr_end that can deal with 64bit addresses */
> +#define kvm_pgd_addr_end(addr, end)					\
> +({	u64 __boundary = ((addr) + PGDIR_SIZE) & PGDIR_MASK;		\
> +	(__boundary - 1 < (end) - 1)? __boundary: (end);		\
> +})
> +
>  struct kvm;
>  
>  static inline void coherent_cache_guest_page(struct kvm_vcpu *vcpu, hva_t hva,
> @@ -142,6 +148,8 @@ static inline void coherent_cache_guest_page(struct kvm_vcpu *vcpu, hva_t hva,
>  #define kvm_flush_dcache_to_poc(a,l)	__cpuc_flush_dcache_area((a), (l))
>  #define kvm_virt_to_phys(x)		virt_to_idmap((unsigned long)(x))
>  
> +void stage2_flush_vm(struct kvm *kvm);
> +
>  #endif	/* !__ASSEMBLY__ */
>  
>  #endif /* __ARM_KVM_MMU_H__ */
> diff --git a/arch/arm/kvm/mmu.c b/arch/arm/kvm/mmu.c
> index fc71a8d..ea21b6a 100644
> --- a/arch/arm/kvm/mmu.c
> +++ b/arch/arm/kvm/mmu.c
> @@ -187,6 +187,99 @@ static void unmap_range(struct kvm *kvm, pgd_t *pgdp,
>  	}
>  }
>  
> +static void stage2_flush_ptes(struct kvm *kvm, pmd_t *pmd,
> +			      phys_addr_t addr, phys_addr_t end)
> +{
> +	pte_t *pte;
> +
> +	pte = pte_offset_kernel(pmd, addr);
> +	do {
> +		if (!pte_none(*pte)) {
> +			hva_t hva = gfn_to_hva(kvm, addr >> PAGE_SHIFT);
> +			kvm_flush_dcache_to_poc((void*)hva, PAGE_SIZE);
> +		}
> +	} while (pte++, addr += PAGE_SIZE, addr != end);
> +}
> +
> +static void stage2_flush_pmds(struct kvm *kvm, pud_t *pud,
> +			      phys_addr_t addr, phys_addr_t end)
> +{
> +	pmd_t *pmd;
> +	phys_addr_t next;
> +
> +	pmd = pmd_offset(pud, addr);
> +	do {
> +		next = pmd_addr_end(addr, end);
> +		if (!pmd_none(*pmd)) {
> +			if (kvm_pmd_huge(*pmd)) {
> +				hva_t hva = gfn_to_hva(kvm, addr >> PAGE_SHIFT);
> +				kvm_flush_dcache_to_poc((void*)hva, PMD_SIZE);
> +			} else {
> +				stage2_flush_ptes(kvm, pmd, addr, next);
> +			}
> +		}
> +	} while (pmd++, addr = next, addr != end);
> +}
> +
> +static void stage2_flush_puds(struct kvm *kvm, pgd_t *pgd,
> +			      phys_addr_t addr, phys_addr_t end)
> +{
> +	pud_t *pud;
> +	phys_addr_t next;
> +
> +	pud = pud_offset(pgd, addr);
> +	do {
> +		next = pud_addr_end(addr, end);
> +		if (!pud_none(*pud)) {
> +			if (pud_huge(*pud)) {
> +				hva_t hva = gfn_to_hva(kvm, addr >> PAGE_SHIFT);
> +				kvm_flush_dcache_to_poc((void*)hva, PUD_SIZE);
> +			} else {
> +				stage2_flush_pmds(kvm, pud, addr, next);
> +			}
> +		}
> +	} while(pud++, addr = next, addr != end);

you missed one space after this while, but no need to respin just
because of that.

> +}
> +
> +static void stage2_flush_memslot(struct kvm *kvm,
> +				 struct kvm_memory_slot *memslot)
> +{
> +	phys_addr_t addr = memslot->base_gfn << PAGE_SHIFT;
> +	phys_addr_t end = addr + PAGE_SIZE * memslot->npages;
> +	phys_addr_t next;
> +	pgd_t *pgd;
> +
> +	pgd = kvm->arch.pgd + pgd_index(addr);
> +	do {
> +		next = kvm_pgd_addr_end(addr, end);
> +		stage2_flush_puds(kvm, pgd, addr, next);
> +	} while (pgd++, addr = next, addr != end);
> +}
> +
> +/**
> + * stage2_flush_vm - Invalidate cache for pages mapped in stage 2
> + * @kvm: The struct kvm pointer
> + *
> + * Go through the stage 2 page tables and invalidate any cache lines
> + * backing memory already mapped to the VM.
> + */
> +void stage2_flush_vm(struct kvm *kvm)
> +{
> +	struct kvm_memslots *slots;
> +	struct kvm_memory_slot *memslot;
> +	int idx;
> +
> +	idx = srcu_read_lock(&kvm->srcu);
> +	spin_lock(&kvm->mmu_lock);
> +
> +	slots = kvm_memslots(kvm);
> +	kvm_for_each_memslot(memslot, slots)
> +		stage2_flush_memslot(kvm, memslot);
> +
> +	spin_unlock(&kvm->mmu_lock);
> +	srcu_read_unlock(&kvm->srcu, idx);
> +}
> +
>  /**
>   * free_boot_hyp_pgd - free HYP boot page tables
>   *
> diff --git a/arch/arm64/include/asm/kvm_mmu.h b/arch/arm64/include/asm/kvm_mmu.h
> index 6eaf69b..e78d050 100644
> --- a/arch/arm64/include/asm/kvm_mmu.h
> +++ b/arch/arm64/include/asm/kvm_mmu.h
> @@ -121,6 +121,8 @@ static inline void kvm_set_s2pmd_writable(pmd_t *pmd)
>  	pmd_val(*pmd) |= PMD_S2_RDWR;
>  }
>  
> +#define kvm_pgd_addr_end(addr, end)	pgd_addr_end(addr, end)
> +
>  struct kvm;
>  
>  #define kvm_flush_dcache_to_poc(a,l)	__flush_dcache_area((a), (l))
> @@ -146,5 +148,7 @@ static inline void coherent_cache_guest_page(struct kvm_vcpu *vcpu, hva_t hva,
>  
>  #define kvm_virt_to_phys(x)		__virt_to_phys((unsigned long)(x))
>  
> +void stage2_flush_vm(struct kvm *kvm);
> +
>  #endif /* __ASSEMBLY__ */
>  #endif /* __ARM64_KVM_MMU_H__ */
> diff --git a/arch/arm64/kvm/sys_regs.c b/arch/arm64/kvm/sys_regs.c
> index 2097e5e..0324458 100644
> --- a/arch/arm64/kvm/sys_regs.c
> +++ b/arch/arm64/kvm/sys_regs.c
> @@ -27,6 +27,7 @@
>  #include <asm/kvm_host.h>
>  #include <asm/kvm_emulate.h>
>  #include <asm/kvm_coproc.h>
> +#include <asm/kvm_mmu.h>
>  #include <asm/cacheflush.h>
>  #include <asm/cputype.h>
>  #include <trace/events/kvm.h>
> @@ -154,8 +155,10 @@ static bool access_sctlr(struct kvm_vcpu *vcpu,
>  {
>  	access_vm_reg(vcpu, p, r);
>  
> -	if (vcpu_has_cache_enabled(vcpu))	/* MMU+Caches enabled? */
> +	if (vcpu_has_cache_enabled(vcpu)) {	/* MMU+Caches enabled? */
>  		vcpu->arch.hcr_el2 &= ~HCR_TVM;
> +		stage2_flush_vm(vcpu->kvm);
> +	}
>  
>  	return true;
>  }
> -- 
> 1.8.3.4
> 

Reviewed-by: Christoffer Dall <[email-masked]>