From: Marc Zyngier <maz@kernel.org>
To: Chenxu Wang <irakatz51@gmail.com>
Cc: kvmarm@lists.cs.columbia.edu
Subject: Re: Problems about Stage-2 translation
Date: Sat, 16 Oct 2021 22:19:38 +0100 [thread overview]
Message-ID: <877decvf9x.wl-maz@kernel.org> (raw)
In-Reply-To: <CAFLP=uDhb8Zq5pAnTbvXi_OU047Uw3WRkw2YJsYNEsCkdHzkJQ@mail.gmail.com>
On Sat, 16 Oct 2021 13:21:01 +0100,
Chenxu Wang <irakatz51@gmail.com> wrote:
>
> Hi all,
>
> I am facing two problems with the Stage-2 translation in KVM.
>
> (1)
> I reserve a memory region (e.g., 0xa000_0000 ~ 0xa020_0000) from DRAM space
> of HostOS, and fill it with some values. Then ask a GuestVM to access this
> region.
>
> void __iomem *region=ioremap(0xa0000000, 0x1000);
> uint32_t val=ioread32(region);
>
> But I get value 0, which is not the expected value.
It is the expected behaviour.
> I guess the reason is that the Stage-2 translation of the GuestVM does not
> map the reserved region, but it should return a translation fault, rather
> than 0. So I feel confused, could you provide some helpful explanation?
Why should the guest see a translation fault? After all, the whole
point of KVM is to transparently handle the translation fault and map
a page on demand.
> (2)
> I consider mapping a region with the Stage-2 translation. I find that KVM
> create the stage-2 table with kvm_alloc_stage2_pgd(). But I could not find
> a function that can "arbitrarily add a stage-2 mapping to the physical
> address in HostOS" when the VM is activated.
>
> Could you provide such functions?
Follow the translation fault path in KVM, and you will find what you
are asking for.
M.
--
Without deviation from the norm, progress is not possible.
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next prev parent reply other threads:[~2021-10-16 21:19 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-10-16 12:21 Problems about Stage-2 translation Chenxu Wang
2021-10-16 21:19 ` Marc Zyngier [this message]
2021-10-18 8:36 ` Chenxu Wang
2021-10-18 10:06 ` Marc Zyngier
2021-10-18 19:01 ` Chenxu Wang
2021-10-18 19:31 ` Marc Zyngier
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