Messages in this thread | | | Subject | Re: [PATCH v1 09/16] kvm: arm/arm64: Delay stage2 page table allocation | From | Suzuki K Poulose <> | Date | Thu, 8 Feb 2018 17:20:57 +0000 |
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On 08/02/18 11:01, Christoffer Dall wrote: > On Tue, Jan 09, 2018 at 07:04:04PM +0000, Suzuki K Poulose wrote: >> We allocate the entry level page tables for stage2 when the >> VM is created. This doesn't give us the flexibility of configuring >> the physical address space size for a VM. In order to allow >> the VM to choose the required size, we delay the allocation of >> stage2 entry level tables until we really try to map something. >> >> This could be either when the VM creates a memory range or when >> it tries to map a device memory. So we add in a hook to these >> two places to make sure the tables are allocated. We use >> kvm->slots_lock to serialize the allocation entry point, since >> we add hooks to the arch specific call back with the mutex held.
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>> >> -/** >> - * kvm_phys_addr_ioremap - map a device range to guest IPA >> - * >> - * @kvm: The KVM pointer >> - * @guest_ipa: The IPA at which to insert the mapping >> - * @pa: The physical address of the device >> - * @size: The size of the mapping >> +/* >> + * Finalise the stage2 page table layout. Must be called with kvm->slots_lock >> + * held. >> */ >> -int kvm_phys_addr_ioremap(struct kvm *kvm, phys_addr_t guest_ipa, >> +static int __kvm_init_stage2_table(struct kvm *kvm) >> +{ >> + /* Double check if somebody has already allocated it */ > > dubious comment: Either leave it out or explain that we need to check > again with the mutex held. > >> + if (likely(kvm->arch.pgd)) >> + return 0; >> + return kvm_alloc_stage2_pgd(kvm); >> +} >> + >> +static int kvm_init_stage2_table(struct kvm *kvm) >> +{ >> + int rc; >> + >> + /* >> + * Once allocated, the stage2 entry level tables are only >> + * freed when the KVM instance is destroyed. So, if we see >> + * something valid here, that guarantees that we have >> + * done the one time allocation and it is something valid >> + * and won't go away until the last reference to the KVM >> + * is gone. >> + */ > > Really not sure if this comment adds something beyond what's described > by the code already?
Agreed. Will clean it up.
Thanks
Suzuki
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