Re: [PATCH v2 17/43] arm64: RME: Allow VMM to set RIPAS

[Suzuki K Poulose <suzuki.poulose@arm.com>]

On 19/04/2024 10:34, Suzuki K Poulose wrote:
> On 12/04/2024 09:42, Steven Price wrote:
>> Each page within the protected region of the realm guest can be marked
>> as either RAM or EMPTY. Allow the VMM to control this before the guest
>> has started and provide the equivalent functions to change this (with
>> the guest's approval) at runtime.
>>
>> When transitioning from RIPAS RAM (1) to RIPAS EMPTY (0) the memory is
>> unmapped from the guest and undelegated allowing the memory to be reused
>> by the host. When transitioning to RIPAS RAM the actual population of
>> the leaf RTTs is done later on stage 2 fault, however it may be
>> necessary to allocate additional RTTs to represent the range requested.
> 
> minor nit: To give a bit more context:
> 
> "however it may be necessary to allocate additional RTTs in order for
> the RMM to track the RIPAS for the requested range".
> 
>>
>> When freeing a block mapping it is necessary to temporarily unfold the
>> RTT which requires delegating an extra page to the RMM, this page can
>> then be recovered once the contents of the block mapping have been
>> freed. A spare, delegated page (spare_page) is used for this purpose.
>>
>> Signed-off-by: Steven Price <steven.price@arm.com>
>> ---
>>   arch/arm64/include/asm/kvm_rme.h |  16 ++
>>   arch/arm64/kvm/mmu.c             |   8 +-
>>   arch/arm64/kvm/rme.c             | 390 +++++++++++++++++++++++++++++++
>>   3 files changed, 411 insertions(+), 3 deletions(-)
>>
>> diff --git a/arch/arm64/include/asm/kvm_rme.h 
>> b/arch/arm64/include/asm/kvm_rme.h
>> index 915e76068b00..cc8f81cfc3c0 100644
>> --- a/arch/arm64/include/asm/kvm_rme.h
>> +++ b/arch/arm64/include/asm/kvm_rme.h
>> @@ -96,6 +96,14 @@ void kvm_realm_destroy_rtts(struct kvm *kvm, u32 
>> ia_bits);
>>   int kvm_create_rec(struct kvm_vcpu *vcpu);
>>   void kvm_destroy_rec(struct kvm_vcpu *vcpu);
>> +void kvm_realm_unmap_range(struct kvm *kvm,
>> +               unsigned long ipa,
>> +               u64 size,
>> +               bool unmap_private);
>> +int realm_set_ipa_state(struct kvm_vcpu *vcpu,
>> +            unsigned long addr, unsigned long end,
>> +            unsigned long ripas);
>> +
>>   #define RME_RTT_BLOCK_LEVEL    2
>>   #define RME_RTT_MAX_LEVEL    3
>> @@ -114,4 +122,12 @@ static inline unsigned long 
>> rme_rtt_level_mapsize(int level)
>>       return (1UL << RME_RTT_LEVEL_SHIFT(level));
>>   }
>> +static inline bool realm_is_addr_protected(struct realm *realm,
>> +                       unsigned long addr)
>> +{
>> +    unsigned int ia_bits = realm->ia_bits;
>> +
>> +    return !(addr & ~(BIT(ia_bits - 1) - 1));
>> +}
>> +
>>   #endif
>> diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c
>> index 46f0c4e80ace..8a7b5449697f 100644
>> --- a/arch/arm64/kvm/mmu.c
>> +++ b/arch/arm64/kvm/mmu.c
>> @@ -310,6 +310,7 @@ static void invalidate_icache_guest_page(void *va, 
>> size_t size)
>>    * @start: The intermediate physical base address of the range to unmap
>>    * @size:  The size of the area to unmap
>>    * @may_block: Whether or not we are permitted to block
>> + * @only_shared: If true then protected mappings should not be unmapped
>>    *
>>    * Clear a range of stage-2 mappings, lowering the various 
>> ref-counts.  Must
>>    * be called while holding mmu_lock (unless for freeing the stage2 
>> pgd before
>> @@ -317,7 +318,7 @@ static void invalidate_icache_guest_page(void *va, 
>> size_t size)
>>    * with things behind our backs.
>>    */
>>   static void __unmap_stage2_range(struct kvm_s2_mmu *mmu, phys_addr_t 
>> start, u64 size,
>> -                 bool may_block)
>> +                 bool may_block, bool only_shared)
>>   {
>>       struct kvm *kvm = kvm_s2_mmu_to_kvm(mmu);
>>       phys_addr_t end = start + size;
>> @@ -330,7 +331,7 @@ static void __unmap_stage2_range(struct kvm_s2_mmu 
>> *mmu, phys_addr_t start, u64
>>   static void unmap_stage2_range(struct kvm_s2_mmu *mmu, phys_addr_t 
>> start, u64 size)
>>   {
>> -    __unmap_stage2_range(mmu, start, size, true);
>> +    __unmap_stage2_range(mmu, start, size, true, false);
>>   }
>>   static void stage2_flush_memslot(struct kvm *kvm,
>> @@ -1771,7 +1772,8 @@ bool kvm_unmap_gfn_range(struct kvm *kvm, struct 
>> kvm_gfn_range *range)
>>       __unmap_stage2_range(&kvm->arch.mmu, range->start << PAGE_SHIFT,
>>                    (range->end - range->start) << PAGE_SHIFT,
>> -                 range->may_block);
>> +                 range->may_block,
>> +                 range->only_shared);
>>       return false;
>>   }
>> diff --git a/arch/arm64/kvm/rme.c b/arch/arm64/kvm/rme.c
>> index 629a095bea61..9e5983c51393 100644
>> --- a/arch/arm64/kvm/rme.c
>> +++ b/arch/arm64/kvm/rme.c
>> @@ -79,6 +79,12 @@ static phys_addr_t __alloc_delegated_page(struct 
>> realm *realm,
>>       return phys;
>>   }
>> +static phys_addr_t alloc_delegated_page(struct realm *realm,
>> +                    struct kvm_mmu_memory_cache *mc)
>> +{
>> +    return __alloc_delegated_page(realm, mc, GFP_KERNEL);
>> +}
>> +
>>   static void free_delegated_page(struct realm *realm, phys_addr_t phys)
>>   {
>>       if (realm->spare_page == PHYS_ADDR_MAX) {
>> @@ -94,6 +100,151 @@ static void free_delegated_page(struct realm 
>> *realm, phys_addr_t phys)
>>       free_page((unsigned long)phys_to_virt(phys));
>>   }
>> +static int realm_rtt_create(struct realm *realm,
>> +                unsigned long addr,
>> +                int level,
>> +                phys_addr_t phys)
>> +{
>> +    addr = ALIGN_DOWN(addr, rme_rtt_level_mapsize(level - 1));
>> +    return rmi_rtt_create(virt_to_phys(realm->rd), phys, addr, level);
>> +}
>> +
>> +static int realm_rtt_fold(struct realm *realm,
>> +              unsigned long addr,
>> +              int level,
>> +              phys_addr_t *rtt_granule)
>> +{
>> +    unsigned long out_rtt;
>> +    int ret;
>> +
>> +    ret = rmi_rtt_fold(virt_to_phys(realm->rd), addr, level, &out_rtt);
>> +
>> +    if (RMI_RETURN_STATUS(ret) == RMI_SUCCESS && rtt_granule)
>> +        *rtt_granule = out_rtt;
>> +
>> +    return ret;
>> +}
>> +
>> +static int realm_destroy_protected(struct realm *realm,
>> +                   unsigned long ipa,
>> +                   unsigned long *next_addr)
>> +{
>> +    unsigned long rd = virt_to_phys(realm->rd);
>> +    unsigned long addr;
>> +    phys_addr_t rtt;
>> +    int ret;
>> +
>> +loop:
>> +    ret = rmi_data_destroy(rd, ipa, &addr, next_addr);
>> +    if (RMI_RETURN_STATUS(ret) == RMI_ERROR_RTT) {
>> +        if (*next_addr > ipa)
>> +            return 0; /* UNASSIGNED */
>> +        rtt = alloc_delegated_page(realm, NULL);
>> +        if (WARN_ON(rtt == PHYS_ADDR_MAX))
>> +            return -1;
>> +        /* ASSIGNED - ipa is mapped as a block, so split */
>> +        ret = realm_rtt_create(realm, ipa,
>> +                       RMI_RETURN_INDEX(ret) + 1, rtt);
> 
> Could we not go all the way to L3 (rather than 1 level deeper) and try
> again ? That way, we are covered for block mappings at L1 (1G).
> 
>> +        if (WARN_ON(ret)) {
>> +            free_delegated_page(realm, rtt);
>> +            return -1;
>> +        }
>> +        /* retry */
>> +        goto loop;
>> +    } else if (WARN_ON(ret)) {
>> +        return -1;
>> +    }
>> +    ret = rmi_granule_undelegate(addr);
>> +
>> +    /*
>> +     * If the undelegate fails then something has gone seriously
>> +     * wrong: take an extra reference to just leak the page
>> +     */
>> +    if (WARN_ON(ret))
>> +        get_page(phys_to_page(addr));
>> +
>> +    return 0;
>> +}
>> +
>> +static void realm_unmap_range_shared(struct kvm *kvm,
>> +                     int level,
>> +                     unsigned long start,
>> +                     unsigned long end)
>> +{
>> +    struct realm *realm = &kvm->arch.realm;
>> +    unsigned long rd = virt_to_phys(realm->rd);
>> +    ssize_t map_size = rme_rtt_level_mapsize(level);
>> +    unsigned long next_addr, addr;
>> +    unsigned long shared_bit = BIT(realm->ia_bits - 1);
>> +
>> +    if (WARN_ON(level > RME_RTT_MAX_LEVEL))
>> +        return;
>> +
>> +    start |= shared_bit;
>> +    end |= shared_bit;
>> +
>> +    for (addr = start; addr < end; addr = next_addr) {
>> +        unsigned long align_addr = ALIGN(addr, map_size);
>> +        int ret;
>> +
>> +        next_addr = ALIGN(addr + 1, map_size);
>> +
>> +        if (align_addr != addr || next_addr > end) {
>> +            /* Need to recurse deeper */
>> +            if (addr < align_addr)
>> +                next_addr = align_addr;
>> +            realm_unmap_range_shared(kvm, level + 1, addr,
>> +                         min(next_addr, end));
>> +            continue;
>> +        }
>> +
>> +        ret = rmi_rtt_unmap_unprotected(rd, addr, level, &next_addr);
> 
> minor nit: We could potentially use rmi_rtt_destroy() to tear down
> shared mappings without unmapping them individually, if the range
> is big enough. All such optimisations could come later though.
> 
>> +        switch (RMI_RETURN_STATUS(ret)) {
>> +        case RMI_SUCCESS:
>> +            break;
>> +        case RMI_ERROR_RTT:
>> +            if (next_addr == addr) {
> 
> At this point we have a block aligned address, but the mapping is
> further deep. Given, start from top to down, we implicitly handle
> the case of block mappings. Not sure if that needs to be in a comment
> here.
> 
>> +                next_addr = ALIGN(addr + 1, map_size);
> 
> Reset to the "actual next" as it was overwritten by the RMI call.
> 
>> +                realm_unmap_range_shared(kvm, level + 1, addr,
>> +                             next_addr);
>> +            }
>> +            break;
>> +        default:
>> +            WARN_ON(1);
>> +        }
>> +    }
>> +}
>> +
>> +static void realm_unmap_range_private(struct kvm *kvm,
>> +                      unsigned long start,
>> +                      unsigned long end)
>> +{
>> +    struct realm *realm = &kvm->arch.realm;
>> +    ssize_t map_size = RME_PAGE_SIZE;
>> +    unsigned long next_addr, addr;
>> +
>> +    for (addr = start; addr < end; addr = next_addr) {
>> +        int ret;
>> +
>> +        next_addr = ALIGN(addr + 1, map_size);
>> +
>> +        ret = realm_destroy_protected(realm, addr, &next_addr);
>> +
>> +        if (WARN_ON(ret))
>> +            break;
>> +    }
>> +}
>> +
>> +static void realm_unmap_range(struct kvm *kvm,
>> +                  unsigned long start,
>> +                  unsigned long end,
>> +                  bool unmap_private)
>> +{
>> +    realm_unmap_range_shared(kvm, RME_RTT_MAX_LEVEL - 1, start, end);
> 
> minor nit: We already have a helper to find a suitable start level
> (defined below), may be we could use that ? And even do the rtt_destroy 
> optimisation for unprotected range.
> 
>> +    if (unmap_private)
>> +        realm_unmap_range_private(kvm, start, end);
>> +}
>> +
>>   u32 kvm_realm_ipa_limit(void)
>>   {
>>       return u64_get_bits(rmm_feat_reg0, RMI_FEATURE_REGISTER_0_S2SZ);
>> @@ -190,6 +341,30 @@ static int realm_rtt_destroy(struct realm *realm, 
>> unsigned long addr,
>>       return ret;
>>   }
>> +static int realm_create_rtt_levels(struct realm *realm,
>> +                   unsigned long ipa,
>> +                   int level,
>> +                   int max_level,
>> +                   struct kvm_mmu_memory_cache *mc)
>> +{
>> +    if (WARN_ON(level == max_level))
>> +        return 0;
>> +
>> +    while (level++ < max_level) {
>> +        phys_addr_t rtt = alloc_delegated_page(realm, mc);
>> +
>> +        if (rtt == PHYS_ADDR_MAX)
>> +            return -ENOMEM;
>> +
>> +        if (realm_rtt_create(realm, ipa, level, rtt)) {
>> +            free_delegated_page(realm, rtt);
>> +            return -ENXIO;
>> +        }
>> +    }
>> +
>> +    return 0;
>> +}
>> +
>>   static int realm_tear_down_rtt_level(struct realm *realm, int level,
>>                        unsigned long start, unsigned long end)
>>   {
>> @@ -265,6 +440,68 @@ static int realm_tear_down_rtt_range(struct realm 
>> *realm,
>>                        start, end);
>>   }
>> +/*
>> + * Returns 0 on successful fold, a negative value on error, a 
>> positive value if
>> + * we were not able to fold all tables at this level.
>> + */
>> +static int realm_fold_rtt_level(struct realm *realm, int level,
>> +                unsigned long start, unsigned long end)
>> +{
>> +    int not_folded = 0;
>> +    ssize_t map_size;
>> +    unsigned long addr, next_addr;
>> +
>> +    if (WARN_ON(level > RME_RTT_MAX_LEVEL))
>> +        return -EINVAL;
>> +
>> +    map_size = rme_rtt_level_mapsize(level - 1);
>> +
>> +    for (addr = start; addr < end; addr = next_addr) {
>> +        phys_addr_t rtt_granule;
>> +        int ret;
>> +        unsigned long align_addr = ALIGN(addr, map_size);
>> +
>> +        next_addr = ALIGN(addr + 1, map_size);
>> +
>> +        ret = realm_rtt_fold(realm, align_addr, level, &rtt_granule);
>> +
>> +        switch (RMI_RETURN_STATUS(ret)) {
>> +        case RMI_SUCCESS:
>> +            if (!WARN_ON(rmi_granule_undelegate(rtt_granule)))
>> +                free_page((unsigned long)phys_to_virt(rtt_granule));
> 
> minor nit: Do we need a wrapper function for things like this, abd 
> leaking the page if undelegate fails, something like
> rme_reclaim_delegated_page()  ?
> 
> 
>> +            break;
>> +        case RMI_ERROR_RTT:
>> +            if (level == RME_RTT_MAX_LEVEL ||
>> +                RMI_RETURN_INDEX(ret) < level) {
>> +                not_folded++;
>> +                break;
>> +            }
>> +            /* Recurse a level deeper */
>> +            ret = realm_fold_rtt_level(realm,
>> +                           level + 1,
>> +                           addr,
>> +                           next_addr);
>> +            if (ret < 0)
>> +                return ret;
>> +            else if (ret == 0)
>> +                /* Try again at this level */
>> +                next_addr = addr;
>> +            break;
>> +        default:
>> +            return -ENXIO;
>> +        }
>> +    }
>> +
>> +    return not_folded;
>> +}
>> +
>> +static int realm_fold_rtt_range(struct realm *realm,
>> +                unsigned long start, unsigned long end)
>> +{
>> +    return realm_fold_rtt_level(realm, get_start_level(realm) + 1,
>> +                    start, end);
>> +}
>> +
>>   static void ensure_spare_page(struct realm *realm)
>>   {
>>       phys_addr_t tmp_rtt;
>> @@ -295,6 +532,147 @@ void kvm_realm_destroy_rtts(struct kvm *kvm, u32 
>> ia_bits)
>>       WARN_ON(realm_tear_down_rtt_range(realm, 0, (1UL << ia_bits)));
>>   }
>> +void kvm_realm_unmap_range(struct kvm *kvm, unsigned long ipa, u64 size,
>> +               bool unmap_private)
>> +{
>> +    unsigned long end = ipa + size;
>> +    struct realm *realm = &kvm->arch.realm;
>> +
>> +    end = min(BIT(realm->ia_bits - 1), end);
>> +
>> +    ensure_spare_page(realm);
>> +
>> +    realm_unmap_range(kvm, ipa, end, unmap_private);
>> +
>> +    realm_fold_rtt_range(realm, ipa, end);
> 
> Shouldn't this be :
> 
>      if (unmap_private)
>          realm_fold_rtt_range(realm, ipa, end);
> 
> Also it is fine to reclaim RTTs from the protected space, not the
> unprotected half, as long as we use RTT_DESTROY in unmap_shared routine.

Thinking about this a bit more, we could :
1. Rename this to realm_reclaim_rtts_range()
2. Use "FOLD" vs "DESTROY" depending on the state of the Realm. If the
    realm is DYING (or add a state in the kvm_pgtable_stage2_destroy() to
    indicate that stage2 can now be "destroyed")  and use DESTROY
    wherever it is safe to do so.

Suzuki