From: Marc Zyngier <maz@kernel.org>
To: Santosh Shukla <sashukla@nvidia.com>
Cc: kvm@vger.kernel.org, kvmarm@lists.cs.columbia.edu,
linux-kernel@vger.kernel.org, james.morse@arm.com,
julien.thierry.kdev@gmail.com, suzuki.poulose@arm.com,
linux-arm-kernel@lists.infradead.org, cjia@nvidia.com
Subject: Re: [PATCH] KVM: arm64: Correctly handle the mmio faulting
Date: Fri, 23 Oct 2020 12:29:28 +0100 [thread overview]
Message-ID: <0a239ac4481fa01c8d09cf2e56dfdabe@kernel.org> (raw)
In-Reply-To: <1603297010-18787-1-git-send-email-sashukla@nvidia.com>
Hi Santosh,
Thanks for this.
On 2020-10-21 17:16, Santosh Shukla wrote:
> The Commit:6d674e28 introduces a notion to detect and handle the
> device mapping. The commit checks for the VM_PFNMAP flag is set
> in vma->flags and if set then marks force_pte to true such that
> if force_pte is true then ignore the THP function check
> (/transparent_hugepage_adjust()).
>
> There could be an issue with the VM_PFNMAP flag setting and checking.
> For example consider a case where the mdev vendor driver register's
> the vma_fault handler named vma_mmio_fault(), which maps the
> host MMIO region in-turn calls remap_pfn_range() and maps
> the MMIO's vma space. Where, remap_pfn_range implicitly sets
> the VM_PFNMAP flag into vma->flags.
>
> Now lets assume a mmio fault handing flow where guest first access
> the MMIO region whose 2nd stage translation is not present.
> So that results to arm64-kvm hypervisor executing guest abort handler,
> like below:
>
> kvm_handle_guest_abort() -->
> user_mem_abort()--> {
>
> ...
> 0. checks the vma->flags for the VM_PFNMAP.
> 1. Since VM_PFNMAP flag is not yet set so force_pte _is_ false;
> 2. gfn_to_pfn_prot() -->
> __gfn_to_pfn_memslot() -->
> fixup_user_fault() -->
> handle_mm_fault()-->
> __do_fault() -->
> vma_mmio_fault() --> // vendor's mdev fault
> handler
> remap_pfn_range()--> // Here sets the VM_PFNMAP
> flag into vma->flags.
> 3. Now that force_pte is set to false in step-2),
> will execute transparent_hugepage_adjust() func and
> that lead to Oops [4].
> }
Hmmm. Nice. Any chance you could provide us with an actual reproducer?
>
> The proposition is to check is_iomap flag before executing the THP
> function transparent_hugepage_adjust().
>
> [4] THP Oops:
>> pc: kvm_is_transparent_hugepage+0x18/0xb0
>> ...
>> ...
>> user_mem_abort+0x340/0x9b8
>> kvm_handle_guest_abort+0x248/0x468
>> handle_exit+0x150/0x1b0
>> kvm_arch_vcpu_ioctl_run+0x4d4/0x778
>> kvm_vcpu_ioctl+0x3c0/0x858
>> ksys_ioctl+0x84/0xb8
>> __arm64_sys_ioctl+0x28/0x38
>
> Tested on Huawei Kunpeng Taishan-200 arm64 server, Using VFIO-mdev
> device.
> Linux tip: 583090b1
>
> Fixes: 6d674e28 ("KVM: arm/arm64: Properly handle faulting of device
> mappings")
> Signed-off-by: Santosh Shukla <sashukla@nvidia.com>
> ---
> arch/arm64/kvm/mmu.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c
> index 3d26b47..ff15357 100644
> --- a/arch/arm64/kvm/mmu.c
> +++ b/arch/arm64/kvm/mmu.c
> @@ -1947,7 +1947,7 @@ static int user_mem_abort(struct kvm_vcpu *vcpu,
> phys_addr_t fault_ipa,
> * If we are not forced to use page mapping, check if we are
> * backed by a THP and thus use block mapping if possible.
> */
> - if (vma_pagesize == PAGE_SIZE && !force_pte)
> + if (vma_pagesize == PAGE_SIZE && !force_pte && !is_iomap(flags))
> vma_pagesize = transparent_hugepage_adjust(memslot, hva,
> &pfn, &fault_ipa);
> if (writable)
Why don't you directly set force_pte to true at the point where we
update
the flags? It certainly would be a bit more readable:
diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c
index 3d26b47a1343..7a4ad984d54e 100644
--- a/arch/arm64/kvm/mmu.c
+++ b/arch/arm64/kvm/mmu.c
@@ -1920,6 +1920,7 @@ static int user_mem_abort(struct kvm_vcpu *vcpu,
phys_addr_t fault_ipa,
if (kvm_is_device_pfn(pfn)) {
mem_type = PAGE_S2_DEVICE;
flags |= KVM_S2PTE_FLAG_IS_IOMAP;
+ force_pte = true;
} else if (logging_active) {
/*
* Faults on pages in a memslot with logging enabled
and almost directly applies to what we have queued for 5.10.
Thanks,
M.
--
Jazz is not dead. It just smells funny...
next prev parent reply other threads:[~2020-10-23 11:29 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-10-21 16:16 [PATCH] KVM: arm64: Correctly handle the mmio faulting Santosh Shukla
2020-10-23 11:29 ` Marc Zyngier [this message]
2021-04-21 2:59 ` Keqian Zhu
2021-04-21 6:20 ` Gavin Shan
2021-04-21 6:17 ` Keqian Zhu
2021-04-21 11:59 ` Marc Zyngier
2021-04-22 2:02 ` Gavin Shan
2021-04-22 6:50 ` Marc Zyngier
2021-04-22 7:36 ` Tarun Gupta (SW-GPU)
2021-04-22 8:00 ` Santosh Shukla
2021-04-23 1:06 ` Keqian Zhu
2021-04-23 1:38 ` Gavin Shan
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=0a239ac4481fa01c8d09cf2e56dfdabe@kernel.org \
--to=maz@kernel.org \
--cc=cjia@nvidia.com \
--cc=james.morse@arm.com \
--cc=julien.thierry.kdev@gmail.com \
--cc=kvm@vger.kernel.org \
--cc=kvmarm@lists.cs.columbia.edu \
--cc=linux-arm-kernel@lists.infradead.org \
--cc=linux-kernel@vger.kernel.org \
--cc=sashukla@nvidia.com \
--cc=suzuki.poulose@arm.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).