Subject: [PATCH v14 5/7] KVM: arm: Add initial dirty page locking support

From: [email-masked] (Mario Smarduch)
Date: Mon, 24 Nov 2014 10:44:31 -0800

On 11/22/2014 11:33 AM, Christoffer Dall wrote:
> On Thu, Nov 13, 2014 at 05:57:46PM -0800, Mario Smarduch wrote:
>> Add support for initial write protection of VM memslots. This patch
>> series assumes that huge PUDs will not be used in 2nd stage tables, which is
>> always valid on ARMv7.
>>
>> Signed-off-by: Mario Smarduch <[email-masked]>
>> ---
>>  arch/arm/include/asm/kvm_host.h       |    2 +
>>  arch/arm/include/asm/kvm_mmu.h        |   20 +++++
>>  arch/arm/include/asm/pgtable-3level.h |    1 +
>>  arch/arm/kvm/mmu.c                    |  138 +++++++++++++++++++++++++++++++++
>>  4 files changed, 161 insertions(+)
>>
>> diff --git a/arch/arm/include/asm/kvm_host.h b/arch/arm/include/asm/kvm_host.h
>> index 3da6ea7..8fa6238 100644
>> --- a/arch/arm/include/asm/kvm_host.h
>> +++ b/arch/arm/include/asm/kvm_host.h
>> @@ -245,4 +245,6 @@ static inline void vgic_arch_setup(const struct vgic_params *vgic)
>>  int kvm_perf_init(void);
>>  int kvm_perf_teardown(void);
>>  
>> +void kvm_mmu_wp_memory_region(struct kvm *kvm, int slot);
>> +
>>  #endif /* __ARM_KVM_HOST_H__ */
>> diff --git a/arch/arm/include/asm/kvm_mmu.h b/arch/arm/include/asm/kvm_mmu.h
>> index 5cc0b0f..08ab5e8 100644
>> --- a/arch/arm/include/asm/kvm_mmu.h
>> +++ b/arch/arm/include/asm/kvm_mmu.h
>> @@ -114,6 +114,26 @@ static inline void kvm_set_s2pmd_writable(pmd_t *pmd)
>>  	pmd_val(*pmd) |= L_PMD_S2_RDWR;
>>  }
>>  
>> +static inline void kvm_set_s2pte_readonly(pte_t *pte)
>> +{
>> +	pte_val(*pte) = (pte_val(*pte) & ~L_PTE_S2_RDWR) | L_PTE_S2_RDONLY;
>> +}
>> +
>> +static inline bool kvm_s2pte_readonly(pte_t *pte)
>> +{
>> +	return (pte_val(*pte) & L_PTE_S2_RDWR) == L_PTE_S2_RDONLY;
>> +}
>> +
>> +static inline void kvm_set_s2pmd_readonly(pmd_t *pmd)
>> +{
>> +	pmd_val(*pmd) = (pmd_val(*pmd) & ~L_PMD_S2_RDWR) | L_PMD_S2_RDONLY;
>> +}
>> +
>> +static inline bool kvm_s2pmd_readonly(pmd_t *pmd)
>> +{
>> +	return (pmd_val(*pmd) & L_PMD_S2_RDWR) == L_PMD_S2_RDONLY;
>> +}
>> +
>>  /* Open coded p*d_addr_end that can deal with 64bit addresses */
>>  #define kvm_pgd_addr_end(addr, end)					\
>>  ({	u64 __boundary = ((addr) + PGDIR_SIZE) & PGDIR_MASK;		\
>> diff --git a/arch/arm/include/asm/pgtable-3level.h b/arch/arm/include/asm/pgtable-3level.h
>> index 06e0bc0..d29c880 100644
>> --- a/arch/arm/include/asm/pgtable-3level.h
>> +++ b/arch/arm/include/asm/pgtable-3level.h
>> @@ -130,6 +130,7 @@
>>  #define L_PTE_S2_RDONLY			(_AT(pteval_t, 1) << 6)   /* HAP[1]   */
>>  #define L_PTE_S2_RDWR			(_AT(pteval_t, 3) << 6)   /* HAP[2:1] */
>>  
>> +#define L_PMD_S2_RDONLY			(_AT(pmdval_t, 1) << 6)   /* HAP[1]   */
>>  #define L_PMD_S2_RDWR			(_AT(pmdval_t, 3) << 6)   /* HAP[2:1] */
>>  
>>  /*
>> diff --git a/arch/arm/kvm/mmu.c b/arch/arm/kvm/mmu.c
>> index 16e7994..1e8b6a9 100644
>> --- a/arch/arm/kvm/mmu.c
>> +++ b/arch/arm/kvm/mmu.c
>> @@ -45,6 +45,7 @@ static phys_addr_t hyp_idmap_vector;
>>  #define pgd_order get_order(PTRS_PER_PGD * sizeof(pgd_t))
>>  
>>  #define kvm_pmd_huge(_x)	(pmd_huge(_x) || pmd_trans_huge(_x))
>> +#define kvm_pud_huge(_x)	pud_huge(_x)
>>  
>>  static void kvm_tlb_flush_vmid_ipa(struct kvm *kvm, phys_addr_t ipa)
>>  {
>> @@ -746,6 +747,131 @@ static bool transparent_hugepage_adjust(pfn_t *pfnp, phys_addr_t *ipap)
>>  	return false;
>>  }
>>  
>> +#ifdef CONFIG_ARM
>> +/**
>> + * stage2_wp_ptes - write protect PMD range
>> + * @pmd:	pointer to pmd entry
>> + * @addr:	range start address
>> + * @end:	range end address
>> + */
>> +static void stage2_wp_ptes(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)) {
>> +			if (!kvm_s2pte_readonly(pte))
>> +				kvm_set_s2pte_readonly(pte);
>> +			}
> 
> incorrect indentation of the closing brace
got it.
> 
>> +	} while (pte++, addr += PAGE_SIZE, addr != end);
>> +}
>> +
>> +/**
>> + * stage2_wp_pmds - write protect PUD range
>> + * @pud:	pointer to pud entry
>> + * @addr:	range start address
>> + * @end:	range end address
>> + */
>> +static void stage2_wp_pmds(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 = kvm_pmd_addr_end(addr, end);
>> +		if (!pmd_none(*pmd)) {
>> +			if (kvm_pmd_huge(*pmd)) {
>> +				if (!kvm_s2pmd_readonly(pmd))
>> +					kvm_set_s2pmd_readonly(pmd);
>> +			} else {
>> +				stage2_wp_ptes(pmd, addr, next);
>> +			}
>> +		}
>> +	} while (pmd++, addr = next, addr != end);
>> +}
>> +
>> +/**
>> +  * stage2_wp_puds - write protect PGD range
>> +  * @pgd:	pointer to pgd entry
>> +  * @addr:	range start address
>> +  * @end:	range end address
>> +  *
>> +  * Process PUD entries, for a huge PUD we cause a panic.
>> +  */
>> +static void  stage2_wp_puds(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 = kvm_pud_addr_end(addr, end);
>> +		if (!pud_none(*pud)) {
>> +			/* TODO:PUD not supported, revisit later if supported */
>> +			BUG_ON(kvm_pud_huge(*pud));
>> +			stage2_wp_pmds(pud, addr, next);
>> +		}
>> +	} while (pud++, addr = next, addr != end);
>> +}
>> +
>> +/**
>> + * stage2_wp_range() - write protect stage2 memory region range
>> + * @kvm:	The KVM pointer
>> + * @addr:	Start address of range
>> + * @end:	End address of range
>> + */
>> +static void stage2_wp_range(struct kvm *kvm, phys_addr_t addr, phys_addr_t end)
>> +{
>> +	pgd_t *pgd;
>> +	phys_addr_t next;
>> +
>> +	pgd = kvm->arch.pgd + pgd_index(addr);
>> +	do {
>> +		/*
>> +		 * Release kvm_mmu_lock periodically if the memory region is
>> +		 * large. Otherwise, we may see kernel panics with
>> +		 * CONFIG_DETECT_HUNG_TASK, CONFIG_LOCK_DETECTOR,
>> +		 * CONFIG_LOCK_DEP. Additionally, holding the lock too long
>> +		 * will also starve other vCPUs.
>> +		 */
>> +		if (need_resched() || spin_needbreak(&kvm->mmu_lock))
>> +			cond_resched_lock(&kvm->mmu_lock);
>> +
>> +		next = kvm_pgd_addr_end(addr, end);
>> +		if (pgd_present(*pgd))
>> +			stage2_wp_puds(pgd, addr, next);
>> +	} while (pgd++, addr = next, addr != end);
>> +}
>> +
>> +/**
>> + * kvm_mmu_wp_memory_region() - write protect stage 2 entries for memory slot
>> + * @kvm:	The KVM pointer
>> + * @slot:	The memory slot to write protect
>> + *
>> + * Called to start logging dirty pages after memory region
>> + * KVM_MEM_LOG_DIRTY_PAGES operation is called. After this function returns
>> + * all present PMD and PTEs are write protected in the memory region.
>> + * Afterwards read of dirty page log can be called.
>> + *
>> + * Acquires kvm_mmu_lock. Called with kvm->slots_lock mutex acquired,
>> + * serializing operations for VM memory regions.
>> + */
>> +void kvm_mmu_wp_memory_region(struct kvm *kvm, int slot)
>> +{
>> +	struct kvm_memory_slot *memslot = id_to_memslot(kvm->memslots, slot);
>> +	phys_addr_t start = memslot->base_gfn << PAGE_SHIFT;
>> +	phys_addr_t end = (memslot->base_gfn + memslot->npages) << PAGE_SHIFT;
>> +
>> +	spin_lock(&kvm->mmu_lock);
>> +	stage2_wp_range(kvm, start, end);
>> +	spin_unlock(&kvm->mmu_lock);
>> +	kvm_flush_remote_tlbs(kvm);
>> +}
>> +#endif
>> +
>>  static int user_mem_abort(struct kvm_vcpu *vcpu, phys_addr_t fault_ipa,
>>  			  struct kvm_memory_slot *memslot,
>>  			  unsigned long fault_status)
>> @@ -1129,6 +1255,18 @@ void kvm_arch_commit_memory_region(struct kvm *kvm,
>>  		unmap_stage2_range(kvm, gpa, size);
>>  		spin_unlock(&kvm->mmu_lock);
>>  	}
>> +
>> +#ifdef CONFIG_ARM
>> +	/*
>> +	 * At this point memslot has been committed and there is an
>> +	 * allocated dirty_bitmap[], dirty pages will be be tracked while the
>> +	 * memory slot is write protected.
>> +	 */
>> +	if (change != KVM_MR_DELETE && change != KVM_MR_MOVE &&
>> +					mem->flags & KVM_MEM_LOG_DIRTY_PAGES)
>> +		kvm_mmu_wp_memory_region(kvm, mem->slot);
> 
> What happens if the user moves a memregion and sets the LOG_DIRTY_PAGES
> flag?

Yes I misinterpreted KVM_MR_MOVE, we need to handle initial write protect as
well if logging is enabled since GPA range moved. Reading qemu code led me
to believe scenario is not possible, but yes that's user space policy of no
concern here. Will correct.

Thanks.

> 
>> +#endif
>> +
>>  }
>>  
>>  int kvm_arch_prepare_memory_region(struct kvm *kvm,
>> -- 
>> 1.7.9.5
>>
> 
> Thanks,
> -Christoffer
>