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Message-ID: <40413863-3158-460b-ad7e-e5afdb45b701@arm.com>
Date: Wed, 24 Apr 2024 11:59:34 +0100
From: Steven Price <steven.price@....com>
To: Suzuki K Poulose <suzuki.poulose@....com>, kvm@...r.kernel.org,
kvmarm@...ts.linux.dev
Cc: Catalin Marinas <catalin.marinas@....com>, Marc Zyngier <maz@...nel.org>,
Will Deacon <will@...nel.org>, James Morse <james.morse@....com>,
Oliver Upton <oliver.upton@...ux.dev>, Zenghui Yu <yuzenghui@...wei.com>,
linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
Joey Gouly <joey.gouly@....com>, Alexandru Elisei
<alexandru.elisei@....com>, Christoffer Dall <christoffer.dall@....com>,
Fuad Tabba <tabba@...gle.com>, linux-coco@...ts.linux.dev,
Ganapatrao Kulkarni <gankulkarni@...amperecomputing.com>
Subject: Re: [PATCH v2 13/43] arm64: RME: RTT handling
On 17/04/2024 14:37, Suzuki K Poulose wrote:
> Hi Steven
>
> minort nit, Subject: arm64: RME: RTT tear down
>
> This patch is all about tearing the RTTs, so may be the subject could
> be adjusted accordingly.
Good point, this patch has evolved and is now all about tearing down.
> On 12/04/2024 09:42, Steven Price wrote:
>> The RMM owns the stage 2 page tables for a realm, and KVM must request
>> that the RMM creates/destroys entries as necessary. The physical pages
>> to store the page tables are delegated to the realm as required, and can
>> be undelegated when no longer used.
>>
>> Creating new RTTs is the easy part, tearing down is a little more
>> tricky. The result of realm_rtt_destroy() can be used to effectively
>> walk the tree and destroy the entries (undelegating pages that were
>> given to the realm).
>
> The patch looks functionally correct to me. Some minor style related
> comments below.
>
>> Signed-off-by: Steven Price <steven.price@....com>
>
>> ---
>> arch/arm64/include/asm/kvm_rme.h | 19 ++++
>> arch/arm64/kvm/mmu.c | 6 +-
>> arch/arm64/kvm/rme.c | 171 +++++++++++++++++++++++++++++++
>> 3 files changed, 193 insertions(+), 3 deletions(-)
>>
>> diff --git a/arch/arm64/include/asm/kvm_rme.h
>> b/arch/arm64/include/asm/kvm_rme.h
>> index fba85e9ce3ae..4ab5cb5e91b3 100644
>> --- a/arch/arm64/include/asm/kvm_rme.h
>> +++ b/arch/arm64/include/asm/kvm_rme.h
>> @@ -76,5 +76,24 @@ u32 kvm_realm_ipa_limit(void);
>> int kvm_realm_enable_cap(struct kvm *kvm, struct kvm_enable_cap *cap);
>> int kvm_init_realm_vm(struct kvm *kvm);
>> void kvm_destroy_realm(struct kvm *kvm);
>> +void kvm_realm_destroy_rtts(struct kvm *kvm, u32 ia_bits);
>> +
>> +#define RME_RTT_BLOCK_LEVEL 2
>> +#define RME_RTT_MAX_LEVEL 3
>> +
>> +#define RME_PAGE_SHIFT 12
>> +#define RME_PAGE_SIZE BIT(RME_PAGE_SHIFT)
>> +/* See ARM64_HW_PGTABLE_LEVEL_SHIFT() */
>> +#define RME_RTT_LEVEL_SHIFT(l) \
>> + ((RME_PAGE_SHIFT - 3) * (4 - (l)) + 3)
>> +#define RME_L2_BLOCK_SIZE BIT(RME_RTT_LEVEL_SHIFT(2))
>> +
>> +static inline unsigned long rme_rtt_level_mapsize(int level)
>> +{
>> + if (WARN_ON(level > RME_RTT_MAX_LEVEL))
>> + return RME_PAGE_SIZE;
>> +
>> + return (1UL << RME_RTT_LEVEL_SHIFT(level));
>> +}
>>
>
> super minor nit: We only support 4K for now, so may be could reuse
> the ARM64 generic macro helpers. I am fine either way.
Given we'll likely want to support host granules other than 4k in the
future I'd like to avoid using the generic ones. It's also a clear
signal that the code is referring to the RTTs rather than the host's
page tables.
>
>> #endif
>> diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c
>> index af4564f3add5..46f0c4e80ace 100644
>> --- a/arch/arm64/kvm/mmu.c
>> +++ b/arch/arm64/kvm/mmu.c
>> @@ -1012,17 +1012,17 @@ void stage2_unmap_vm(struct kvm *kvm)
>> void kvm_free_stage2_pgd(struct kvm_s2_mmu *mmu)
>> {
>> struct kvm *kvm = kvm_s2_mmu_to_kvm(mmu);
>> - struct kvm_pgtable *pgt = NULL;
>> + struct kvm_pgtable *pgt;
>> write_lock(&kvm->mmu_lock);
>> + pgt = mmu->pgt;
>> if (kvm_is_realm(kvm) &&
>> (kvm_realm_state(kvm) != REALM_STATE_DEAD &&
>> kvm_realm_state(kvm) != REALM_STATE_NONE)) {
>> - /* TODO: teardown rtts */
>> write_unlock(&kvm->mmu_lock);
>> + kvm_realm_destroy_rtts(kvm, pgt->ia_bits);
>> return;
>> }
>> - pgt = mmu->pgt;
>> if (pgt) {
>> mmu->pgd_phys = 0;
>> mmu->pgt = NULL;
>> diff --git a/arch/arm64/kvm/rme.c b/arch/arm64/kvm/rme.c
>> index 9652ec6ab2fd..09b59bcad8b6 100644
>> --- a/arch/arm64/kvm/rme.c
>> +++ b/arch/arm64/kvm/rme.c
>> @@ -47,6 +47,53 @@ static int rmi_check_version(void)
>> return 0;
>> }
>> +static phys_addr_t __alloc_delegated_page(struct realm *realm,
>> + struct kvm_mmu_memory_cache *mc,
>> + gfp_t flags)
>
> minor nit: Do we need "__" here ? The counter part is plain
> free_delegated_page without the "__". We could drop the prefix
>
> Or we could split the function as:
>
> alloc_delegated_page()
> {
> if (spare_page_available)
> return spare_page;
> return __alloc_delegated_page(); /* Alloc and delegate a page */
> }
I'm not really sure I follow. The reason for the 'wrapper' function
alloc_delegated_page() is because most call sites don't care about the
GFP flags (defaults to GFP_KERNEL), but for ensure_spare_page() we need
to pass GFP_ATOMIC.
Admittedly there are only 3 call sites in total and the wrapper isn't
added yet. I'll tidy this up by simply adding the GFP_KERNEL flag onto
the two call sites.
>
>> +{
>> + phys_addr_t phys = PHYS_ADDR_MAX;
>> + void *virt;
>> +
>> + if (realm->spare_page != PHYS_ADDR_MAX) {
>> + swap(realm->spare_page, phys);
>> + goto out;
>> + }
>> +
>> + if (mc)
>> + virt = kvm_mmu_memory_cache_alloc(mc);
>> + else
>> + virt = (void *)__get_free_page(flags);
>> +
>> + if (!virt)
>> + goto out;
>> +
>> + phys = virt_to_phys(virt);
>> +
>> + if (rmi_granule_delegate(phys)) {
>> + free_page((unsigned long)virt);
>> +
>> + phys = PHYS_ADDR_MAX;
>> + }
>> +
>> +out:
>> + return phys;
>> +}
>> +
>> +static void free_delegated_page(struct realm *realm, phys_addr_t phys)
>> +{
>> + if (realm->spare_page == PHYS_ADDR_MAX) {
>> + realm->spare_page = phys;
>> + return;
>> + }
>> +
>> + if (WARN_ON(rmi_granule_undelegate(phys))) {
>> + /* Undelegate failed: leak the page */
>> + return;
>> + }
>> +
>> + free_page((unsigned long)phys_to_virt(phys));
>> +}
>> +
>> u32 kvm_realm_ipa_limit(void)
>> {
>> return u64_get_bits(rmm_feat_reg0, RMI_FEATURE_REGISTER_0_S2SZ);
>> @@ -124,6 +171,130 @@ static int realm_create_rd(struct kvm *kvm)
>> return r;
>> }
>> +static int realm_rtt_destroy(struct realm *realm, unsigned long addr,
>> + int level, phys_addr_t *rtt_granule,
>> + unsigned long *next_addr)
>> +{
>> + unsigned long out_rtt;
>> + unsigned long out_top;
>> + int ret;
>> +
>> + ret = rmi_rtt_destroy(virt_to_phys(realm->rd), addr, level,
>> + &out_rtt, &out_top);
>> +
>> + if (rtt_granule)
>> + *rtt_granule = out_rtt;
>> + if (next_addr)
>> + *next_addr = out_top;
>
> minor nit: As mentioned in the previous patch, we could move this check
> to the rmi_rtt_destroy().
Done, I've also dropped the check for rtt_granule - it's a bug to be
passing that as NULL.
>> +
>> + return ret;
>> +}
>> +
>> +static int realm_tear_down_rtt_level(struct realm *realm, int level,
>> + unsigned long start, unsigned long end)
>> +{
>> + 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);
>> +
>> + if (next_addr <= end && align_addr == addr) {
>> + ret = realm_rtt_destroy(realm, addr, level,
>> + &rtt_granule, &next_addr);
>> + } else {
>> + /* Recurse a level deeper */
>> + ret = realm_tear_down_rtt_level(realm,
>> + level + 1,
>> + addr,
>> + min(next_addr, end));
>> + if (ret)
>> + return ret;
>> + continue;
>> + }
>
> I think it would be better readable if we did something like :
>
> /*
> * The target range is smaller than what this level
> * covers. Go deeper.
> */
> if (next_addr > end || align_addr != addr) {
> ret = realm_tear_down_rtt_level(realm,
> level + 1, addr,
> min(next_addr, end));
> if (ret)
> return ret;
> continue;
> }
>
> ret = realm_rtt_destroy(realm, addr, level,
> &rtt_granule, &next_addr);
Yes that seems clearly, thanks for the suggestion.
>> +
>> + 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));
>> + break;
>> + case RMI_ERROR_RTT:
>> + if (next_addr > addr) {
>> + /* unassigned or destroyed */
>
> minor nit:
> /* RTT doesn't exist, skip */
Indeed, this comment is out of date - the spec now calls this condition
"Missing RTT" so I'll use that wording.
>
>> + break;
>> + }
>
>> + if (WARN_ON(RMI_RETURN_INDEX(ret) != level))
>> + return -EBUSY;
>
> In practise, we only call this for the full IPA range and we wouldn't go
> deeper, if the top level entry was missing. So, there is no reason why
> the RMM didn't walk to the requested level. May be we could add a
> comment here :
> /*
> * We tear down the RTT range for the full IPA
> * space, after everything is unmapped. Also we
> * descend down only if we cannot tear down a
> * top level RTT. Thus RMM must be able to walk
> * to the requested level. e.g., a block mapping
> * exists at L1 or L2.
> */
Sure, will add.
>> + if (WARN_ON(level == RME_RTT_MAX_LEVEL)) {
>> + // Live entry
>> + return -EBUSY;
>
>
> The first part of the comment above applies to this. So may be it is
> good to have it.
>
>
>> + }
>
>> + /* Recurse a level deeper */
>
> minor nit:
> /*
> * The table has active entries in it, recurse
> * deeper and tear down the RTTs.
> */
Sure
>> + next_addr = ALIGN(addr + 1, map_size);
>> + ret = realm_tear_down_rtt_level(realm,
>> + level + 1,
>> + addr,
>> + next_addr);
>> + if (ret)
>> + return ret;
>> + /* Try again at this level */
>
> /*
> * Now that the children RTTs are destroyed,
> * retry at this level.
> */
Sure
>> + next_addr = addr;
>> + break;
>> + default:
>> + WARN_ON(1);
>> + return -ENXIO;
>> + }
>> + }
>> +
>> + return 0;
>> +}
>> +
>> +static int realm_tear_down_rtt_range(struct realm *realm,
>> + unsigned long start, unsigned long end)
>> +{
>> + return realm_tear_down_rtt_level(realm, get_start_level(realm) + 1,
>> + start, end);
>> +}
>> +
>> +static void ensure_spare_page(struct realm *realm)
>> +{
>> + phys_addr_t tmp_rtt;
>> +
>> + /*
>> + * Make sure we have a spare delegated page for tearing down the
>> + * block mappings. We do this by allocating then freeing a page.
>> + * We must use Atomic allocations as we are called with
>> kvm->mmu_lock
>> + * held.
>> + */
>> + tmp_rtt = __alloc_delegated_page(realm, NULL, GFP_ATOMIC);
>> +
>> + /*
>> + * If the allocation failed, continue as we may not have a block
>> level
>> + * mapping so it may not be fatal, otherwise free it to assign it
>> + * to the spare page.
>> + */
>> + if (tmp_rtt != PHYS_ADDR_MAX)
>> + free_delegated_page(realm, tmp_rtt);
>> +}
>> +
>> +void kvm_realm_destroy_rtts(struct kvm *kvm, u32 ia_bits)
>> +{
>> + struct realm *realm = &kvm->arch.realm;
>> +
>> + ensure_spare_page(realm);
>> +
>> + WARN_ON(realm_tear_down_rtt_range(realm, 0, (1UL << ia_bits)));
>> +}
>
> minor nit: We don't seem to be using the "spare_page" yet in this patch.
> May be a good idea to move all the related changes
> (alloc_delegated_page() / free_delegated_page, ensure_spare_page() etc)
> to the patch where it may be better suited ?
Good point - I think the calls get added in "arm64: RME: Allow VMM to
set RIPAS". I'll try to move them there.
Thanks,
Steve
> Suzuki
>
>> +
>> /* Protects access to rme_vmid_bitmap */
>> static DEFINE_SPINLOCK(rme_vmid_lock);
>> static unsigned long *rme_vmid_bitmap;
>
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