Re: [PATCH 03/26] KVM: arm64: Factor out stage 2 page table data from struct kvm

James Morse
2020-05-05T16:03:31Z

Hi Marc,

On 22/04/2020 13:00, Marc Zyngier wrote:
> From: Christoffer Dall <christoffer.dall@arm.com>
>
> As we are about to reuse our stage 2 page table manipulation code for
> shadow stage 2 page tables in the context of nested virtualization, we
> are going to manage multiple stage 2 page tables for a single VM.
>
> This requires some pretty invasive changes to our data structures,
> which moves the vmid and pgd pointers into a separate structure and
> change pretty much all of our mmu code to operate on this structure
> instead.
>
> The new structure is called struct kvm_s2_mmu.
>
> There is no intended functional change by this patch alone.

It's not obvious to me that VTCR_EL2.T0SZ is a per-vm thing, today the size of the IPA
space comes from the VMM, its not a hardware/compile-time property. Where does the vEL2's
T0SZ go? ... but using this for nested guests would 'only' cause a translation fault, it
would still need handling in the emulation code. So making it per-vm should be simpler.

But accessing VTCR is why the stage2_dissolve_p?d() stuff still needs the kvm pointer,
hence the backreference... it might be neater to push the vtcr properties into kvm_s2_mmu
that way you could drop the kvm backref, and only things that take vm-wide locks would
need the kvm pointer. But I don't think it matters.

I think I get it. I can't see anything that should be the other vm/vcpu pointer.

Reviewed-by: James Morse <james.morse@arm.com>

Some boring fiddly stuff:

[...]

> @@ -125,24 +123,24 @@ static void __hyp_text __tlb_switch_to_host_nvhe(struct kvm *kvm,
> }
> }
>
> -static void __hyp_text __tlb_switch_to_host(struct kvm *kvm,
> +static void __hyp_text __tlb_switch_to_host(struct kvm_s2_mmu *mmu,
> struct tlb_inv_context *cxt)
> {
> if (has_vhe())
> - __tlb_switch_to_host_vhe(kvm, cxt);
> + __tlb_switch_to_host_vhe(cxt);
> else
> - __tlb_switch_to_host_nvhe(kvm, cxt);
> + __tlb_switch_to_host_nvhe(cxt);
> }

What does __tlb_switch_to_host() need the kvm_s2_mmu for?

[...]

> void __hyp_text __kvm_tlb_flush_local_vmid(struct kvm_vcpu *vcpu)
> {
> - struct kvm *kvm = kern_hyp_va(kern_hyp_va(vcpu)->kvm);
> + struct kvm_s2_mmu *mmu = kern_hyp_va(kern_hyp_va(vcpu)->arch.hw_mmu);
> struct tlb_inv_context cxt;
>
> /* Switch to requested VMID */
> - __tlb_switch_to_guest(kvm, &cxt);
> + __tlb_switch_to_guest(mmu, &cxt);
>
> __tlbi(vmalle1);
> dsb(nsh);
> isb();
>
> - __tlb_switch_to_host(kvm, &cxt);
> + __tlb_switch_to_host(mmu, &cxt);
> }

Does this need the vcpu in the future?
Its the odd one out, the other tlb functions here take the s2_mmu, or nothing.
We only use the s2_mmu here.

[...]

> diff --git a/virt/kvm/arm/mmu.c b/virt/kvm/arm/mmu.c
> index e3b9ee268823b..2f99749048285 100644
> --- a/virt/kvm/arm/mmu.c
> +++ b/virt/kvm/arm/mmu.c

> @@ -96,31 +96,33 @@ static bool kvm_is_device_pfn(unsigned long pfn)
> *
> * Function clears a PMD entry, flushes addr 1st and 2nd stage TLBs.
> */
> -static void stage2_dissolve_pmd(struct kvm *kvm, phys_addr_t addr, pmd_t *pmd)
> +static void stage2_dissolve_pmd(struct kvm_s2_mmu *mmu, phys_addr_t addr, pmd_t *pmd)

The comment above this function still has '@kvm: pointer to kvm structure.'

[...]

> @@ -331,8 +339,9 @@ static void unmap_stage2_puds(struct kvm *kvm, pgd_t *pgd,
> * destroying the VM), otherwise another faulting VCPU may come in and mess
> * with things behind our backs.
> */
> -static void unmap_stage2_range(struct kvm *kvm, phys_addr_t start, u64 size)
> +static void unmap_stage2_range(struct kvm_s2_mmu *mmu, phys_addr_t start, u64 size)

The comment above this function still has '@kvm: The VM pointer'

[...]

> -static void stage2_flush_memslot(struct kvm *kvm,
> +static void stage2_flush_memslot(struct kvm_s2_mmu *mmu,
> struct kvm_memory_slot *memslot)
> {

Wouldn't something manipulating a memslot have to mess with a set of kvm_s2_mmu once this
is all assembled?
stage2_unmap_memslot() takes struct kvm, it seems odd to pass one kvm_s2_mmu here.

[...]

> @@ -886,21 +898,23 @@ int create_hyp_exec_mappings(phys_addr_t phys_addr, size_t size,

> -int kvm_alloc_stage2_pgd(struct kvm *kvm)
> +int kvm_init_stage2_mmu(struct kvm *kvm, struct kvm_s2_mmu *mmu)
> {
> phys_addr_t pgd_phys;
> pgd_t *pgd;
> + int cpu;
>
> - if (kvm->arch.pgd != NULL) {
> + if (mmu->pgd != NULL) {
> kvm_err("kvm_arch already initialized?\n");

Does this error message still make sense?

> return -EINVAL;
> }

[...]

> @@ -1439,9 +1467,10 @@ static void stage2_wp_ptes(pmd_t *pmd, phys_addr_t addr, phys_addr_t end)
> * @addr: range start address
> * @end: range end address
> */
> -static void stage2_wp_pmds(struct kvm *kvm, pud_t *pud,
> +static void stage2_wp_pmds(struct kvm_s2_mmu *mmu, pud_t *pud,
> phys_addr_t addr, phys_addr_t end)

The comment above this function still has 'kvm: kvm instance for the VM'.

> {
> + struct kvm *kvm = mmu->kvm;
> pmd_t *pmd;
> phys_addr_t next;
>
> @@ -1461,14 +1490,15 @@ static void stage2_wp_pmds(struct kvm *kvm, pud_t *pud,
> }
>
> /**
> - * stage2_wp_puds - write protect PGD range
> - * @pgd: pointer to pgd entry
> - * @addr: range start address
> - * @end: range end address
> - */
> -static void stage2_wp_puds(struct kvm *kvm, pgd_t *pgd,
> + * stage2_wp_puds - write protect PGD range
> + * @pgd: pointer to pgd entry
> + * @addr: range start address
> + * @end: range end address
> + */
> +static void stage2_wp_puds(struct kvm_s2_mmu *mmu, pgd_t *pgd,
> phys_addr_t addr, phys_addr_t end)

Comment was missing @kvm, now its missing @mmu....

> {
> + struct kvm *kvm __maybe_unused = mmu->kvm;
> pud_t *pud;
> phys_addr_t next;
>

> @@ -1492,12 +1522,13 @@ static void stage2_wp_puds(struct kvm *kvm, pgd_t *pgd,
> * @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)
> +static void stage2_wp_range(struct kvm_s2_mmu *mmu, phys_addr_t addr, phys_addr_t end)

The comment above this function still ... you get the picture.

[...]

Thanks,

James