Re: [RFC PATCH 09/28] arm64: RME: RTT handling

Zhi Wang
2023-03-04T12:32:29Z

On Fri, 3 Mar 2023 14:04:56 +0000
Steven Price <steven.price@arm.com> wrote:

> On 13/02/2023 17:44, Zhi Wang wrote:
> > On Fri, 27 Jan 2023 11:29:13 +0000
> > Steven Price <steven.price@arm.com> 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.
> >>
> >
> > This is only an introduction to RTT handling. While this patch is mostly like
> > RTT teardown, better add more introduction to this patch. Also maybe refine
> > the tittle to reflect what this patch is actually doing.
>
> You've a definite point that this patch is mostly about RTT teardown.
> Technically it also adds the RTT creation path (realm_rtt_create) -
> hence the generic patch title.
>

But realm_rtt_create() seem only used in realm_tear_down_rtt_range(). That
makes me wonder where is the real RTT creation path.

> But I'll definitely expand the commit message to mention the complexity
> of tear down which is the bulk of the patch.

It is also a good place to explain more about the RTT.

>
> >> Signed-off-by: Steven Price <steven.price@arm.com>
> >> ---
> >> arch/arm64/include/asm/kvm_rme.h | 19 +++++
> >> arch/arm64/kvm/mmu.c | 7 +-
> >> arch/arm64/kvm/rme.c | 139 +++++++++++++++++++++++++++++++
> >> 3 files changed, 162 insertions(+), 3 deletions(-)
> >>
> >> diff --git a/arch/arm64/include/asm/kvm_rme.h b/arch/arm64/include/asm/kvm_rme.h
> >> index a6318af3ed11..eea5118dfa8a 100644
> >> --- a/arch/arm64/include/asm/kvm_rme.h
> >> +++ b/arch/arm64/include/asm/kvm_rme.h
> >> @@ -35,5 +35,24 @@ 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 realm *realm, u32 ia_bits, u32 start_level);
> >> +
> >> +#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));
> >> +}
> >>
> >> #endif
> >> diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c
> >> index 22c00274884a..f29558c5dcbc 100644
> >> --- a/arch/arm64/kvm/mmu.c
> >> +++ b/arch/arm64/kvm/mmu.c
> >> @@ -834,16 +834,17 @@ 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_DYING) {
> >> - /* TODO: teardown rtts */
> >> write_unlock(&kvm->mmu_lock);
> >> + kvm_realm_destroy_rtts(&kvm->arch.realm, pgt->ia_bits,
> >> + pgt->start_level);
> >> 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 0c9d70e4d9e6..f7b0e5a779f8 100644
> >> --- a/arch/arm64/kvm/rme.c
> >> +++ b/arch/arm64/kvm/rme.c
> >> @@ -73,6 +73,28 @@ static int rmi_check_version(void)
> >> return 0;
> >> }
> >>
> >> +static void realm_destroy_undelegate_range(struct realm *realm,
> >> + unsigned long ipa,
> >> + unsigned long addr,
> >> + ssize_t size)
> >> +{
> >> + unsigned long rd = virt_to_phys(realm->rd);
> >> + int ret;
> >> +
> >> + while (size > 0) {
> >> + ret = rmi_data_destroy(rd, ipa);
> >> + WARN_ON(ret);
> >> + ret = rmi_granule_undelegate(addr);
> >> +
> > As the return value is not documented, what will happen if a page undelegate
> > failed? Leaked? Some explanation is required here.
>
> Yes - it's leaked. I'll add a comment to explain the get_page() call.
>
> Thanks,
>
> Steve
>
> >> + if (ret)
> >> + get_page(phys_to_page(addr));
> >> +
> >> + addr += PAGE_SIZE;
> >> + ipa += PAGE_SIZE;
> >> + size -= PAGE_SIZE;
> >> + }
> >> +}
> >> +
> >> static unsigned long create_realm_feat_reg0(struct kvm *kvm)
> >> {
> >> unsigned long ia_bits = VTCR_EL2_IPA(kvm->arch.vtcr);
> >> @@ -170,6 +192,123 @@ 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)
> >> +{
> >> + addr = ALIGN_DOWN(addr, rme_rtt_level_mapsize(level - 1));
> >> + return rmi_rtt_destroy(rtt_granule, virt_to_phys(realm->rd), addr,
> >> + level);
> >> +}
> >> +
> >> +static int realm_destroy_free_rtt(struct realm *realm, unsigned long addr,
> >> + int level, phys_addr_t rtt_granule)
> >> +{
> >> + if (realm_rtt_destroy(realm, addr, level, rtt_granule))
> >> + return -ENXIO;
> >> + if (!WARN_ON(rmi_granule_undelegate(rtt_granule)))
> >> + put_page(phys_to_page(rtt_granule));
> >> +
> >> + return 0;
> >> +}
> >> +
> >> +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(phys, virt_to_phys(realm->rd), addr, level);
> >> +}
> >> +
> >> +static int realm_tear_down_rtt_range(struct realm *realm, int level,
> >> + unsigned long start, unsigned long end)
> >> +{
> >> + phys_addr_t rd = virt_to_phys(realm->rd);
> >> + ssize_t map_size = rme_rtt_level_mapsize(level);
> >> + unsigned long addr, next_addr;
> >> + bool failed = false;
> >> +
> >> + for (addr = start; addr < end; addr = next_addr) {
> >> + phys_addr_t rtt_addr, tmp_rtt;
> >> + struct rtt_entry rtt;
> >> + unsigned long end_addr;
> >> +
> >> + next_addr = ALIGN(addr + 1, map_size);
> >> +
> >> + end_addr = min(next_addr, end);
> >> +
> >> + if (rmi_rtt_read_entry(rd, ALIGN_DOWN(addr, map_size),
> >> + level, &rtt)) {
> >> + failed = true;
> >> + continue;
> >> + }
> >> +
> >> + rtt_addr = rmi_rtt_get_phys(&rtt);
> >> + WARN_ON(level != rtt.walk_level);
> >> +
> >> + switch (rtt.state) {
> >> + case RMI_UNASSIGNED:
> >> + case RMI_DESTROYED:
> >> + break;
> >> + case RMI_TABLE:
> >> + if (realm_tear_down_rtt_range(realm, level + 1,
> >> + addr, end_addr)) {
> >> + failed = true;
> >> + break;
> >> + }
> >> + if (IS_ALIGNED(addr, map_size) &&
> >> + next_addr <= end &&
> >> + realm_destroy_free_rtt(realm, addr, level + 1,
> >> + rtt_addr))
> >> + failed = true;
> >> + break;
> >> + case RMI_ASSIGNED:
> >> + WARN_ON(!rtt_addr);
> >> + /*
> >> + * If there is a block mapping, break it now, using the
> >> + * spare_page. We are sure to have a valid delegated
> >> + * page at spare_page before we enter here, otherwise
> >> + * WARN once, which will be followed by further
> >> + * warnings.
> >> + */
> >> + tmp_rtt = realm->spare_page;
> >> + if (level == 2 &&
> >> + !WARN_ON_ONCE(tmp_rtt == PHYS_ADDR_MAX) &&
> >> + realm_rtt_create(realm, addr,
> >> + RME_RTT_MAX_LEVEL, tmp_rtt)) {
> >> + WARN_ON(1);
> >> + failed = true;
> >> + break;
> >> + }
> >> + realm_destroy_undelegate_range(realm, addr,
> >> + rtt_addr, map_size);
> >> + /*
> >> + * Collapse the last level table and make the spare page
> >> + * reusable again.
> >> + */
> >> + if (level == 2 &&
> >> + realm_rtt_destroy(realm, addr, RME_RTT_MAX_LEVEL,
> >> + tmp_rtt))
> >> + failed = true;
> >> + break;
> >> + case RMI_VALID_NS:
> >> + WARN_ON(rmi_rtt_unmap_unprotected(rd, addr, level));
> >> + break;
> >> + default:
> >> + WARN_ON(1);
> >> + failed = true;
> >> + break;
> >> + }
> >> + }
> >> +
> >> + return failed ? -EINVAL : 0;
> >> +}
> >> +
> >> +void kvm_realm_destroy_rtts(struct realm *realm, u32 ia_bits, u32 start_level)
> >> +{
> >> + realm_tear_down_rtt_range(realm, start_level, 0, (1UL << ia_bits));
> >> +}
> >> +
> >> /* Protects access to rme_vmid_bitmap */
> >> static DEFINE_SPINLOCK(rme_vmid_lock);
> >> static unsigned long *rme_vmid_bitmap;
> >
>