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SubjectRe: [PATCH v2 02/29] LoongArch: KVM: Implement kvm module related interface
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On 2023/2/21 18:18, maobibo wrote:
>
>
> 在 2023/2/21 16:14, Paolo Bonzini 写道:
>> On 2/21/23 07:59, maobibo wrote:
>>>> Also, why does the world switch code need a copy?
>>> There will be problem in world switch code if there is page fault reenter,
>>> since pgd register is shared between root kernel and kvm hypervisor.
>>> World switch entry need be unmapped area, cannot be tlb mapped area.
>>
>> So if I understand correctly the processor is in direct address translation mode until the "csrwr t0, LOONGARCH_CSR_CRMD" instruction. Where does it leave paged mode?
> The processor still in paged mode during world switch context. For example
> when vm exits from guest mode to root mode, it executes world switch code
> from kvm_vector_entry, PC register points to HVA address, however vmid from
> LOONGARCH_CSR_GTLBC is not clear to root mode. If there is page fault
> exception, hardware treats it exception from GPA-->HPA rather than that
> from HVA --> HPA, since vmid info in CSR_GTLBC is not zero.
>
> In page mode, there are two kinds of address: unmapped address and
> tlb mapped address. For unmapped address there is only cachable/uncachable
> attribution, but not RWX attr; and there is no tlb handling for it.
> For simplicity, unmapped address can be treated as window filtered address.
>
> It will be fully root mode only after this piece of code is executed
> during world switch context; vmid is zero and PC points to HVA.
> ori t0, zero, CSR_GSTAT_PVM
> csrxchg zero, t0, LOONGARCH_CSR_GSTAT
> /* Clear GTLBC.TGID field */
> csrrd t0, LOONGARCH_CSR_GTLBC
> bstrins.w t0, zero, CSR_GTLBC_TGID_SHIFT_END, CSR_GTLBC_TGID_SHIFT
> csrwr t0, LOONGARCH_CSR_GTLBC

AFAIK all of these is probably coming from Volume 3 of LoongArch ISA
Manual, which is unfortunately not publicly available at the moment. For
sake of meaningful reviews, when can we expect to get our hands on the
manuals?

--
WANG "xen0n" Xuerui

Linux/LoongArch mailing list: https://lore.kernel.org/loongarch/

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