KVM ARM Archive on lore.kernel.org
 help / color / Atom feed
From: Marc Zyngier <maz@kernel.org>
To: Steven Price <steven.price@arm.com>
Cc: kvm@vger.kernel.org, Catalin Marinas <catalin.marinas@arm.com>,
	linux-doc@vger.kernel.org, Russell King <linux@armlinux.org.uk>,
	linux-kernel@vger.kernel.org, Paolo Bonzini <pbonzini@redhat.com>,
	Will Deacon <will@kernel.org>,
	kvmarm@lists.cs.columbia.edu,
	linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH 6/9] KVM: arm64: Provide a PV_TIME device to user space
Date: Mon, 5 Aug 2019 17:28:57 +0100
Message-ID: <c18f9d74-48eb-3e03-dca8-ad44e6d6b682@kernel.org> (raw)
In-Reply-To: <1a7d5be6-184b-0c78-61a3-b01730cb5df9@arm.com>

On 05/08/2019 17:10, Steven Price wrote:
> On 03/08/2019 13:51, Marc Zyngier wrote:
>> On Fri,  2 Aug 2019 15:50:14 +0100
>> Steven Price <steven.price@arm.com> wrote:
>>
>>> Allow user space to inform the KVM host where in the physical memory
>>> map the paravirtualized time structures should be located.
>>>
>>> A device is created which provides the base address of an array of
>>> Stolen Time (ST) structures, one for each VCPU. There must be (64 *
>>> total number of VCPUs) bytes of memory available at this location.
>>>
>>> The address is given in terms of the physical address visible to
>>> the guest and must be 64 byte aligned. The memory should be marked as
>>> reserved to the guest to stop it allocating it for other purposes.
>>
>> Why? You seem to be allocating the memory from the kernel, so as far as
>> the guest is concerned, this isn't generally usable memory.
> 
> I obviously didn't word it very well - that's what I meant. The "memory"
> that represents the stolen time structure shouldn't be shown to the
> guest as normal memory, but "reserved" for the purpose of stolen time.
> 
> To be honest it looks like I forgot to rewrite this commit message -
> which 64 byte alignment is all that the guest can rely on (because each
> vCPU has it's own structure), the actual array of structures needs to be
> page aligned to ensure we can safely map it into the guest.
> 
>>>
>>> Signed-off-by: Steven Price <steven.price@arm.com>
>>> ---
>>>  arch/arm64/include/asm/kvm_mmu.h  |   2 +
>>>  arch/arm64/include/uapi/asm/kvm.h |   6 +
>>>  arch/arm64/kvm/Makefile           |   1 +
>>>  include/uapi/linux/kvm.h          |   2 +
>>>  virt/kvm/arm/mmu.c                |  44 +++++++
>>>  virt/kvm/arm/pvtime.c             | 190 ++++++++++++++++++++++++++++++
>>>  6 files changed, 245 insertions(+)
>>>  create mode 100644 virt/kvm/arm/pvtime.c

[...]

>>> +static int kvm_arm_pvtime_set_attr(struct kvm_device *dev,
>>> +				   struct kvm_device_attr *attr)
>>> +{
>>> +	struct kvm_arch_pvtime *pvtime = &dev->kvm->arch.pvtime;
>>> +	u64 __user *user = (u64 __user *)attr->addr;
>>> +	u64 paddr;
>>> +	int ret;
>>> +
>>> +	switch (attr->group) {
>>> +	case KVM_DEV_ARM_PV_TIME_PADDR:
>>> +		if (get_user(paddr, user))
>>> +			return -EFAULT;
>>> +		if (paddr & 63)
>>> +			return -EINVAL;
>>
>> You should check whether the device fits into the IPA space for this
>> guest, and whether it overlaps with anything else.
> 
> pvtime_map_pages() should fail in the case of overlap. That seems
> sufficient to me - do you think we need something stronger?

Definitely. stage2_set_pte() won't fail for a non-IO overlapping
mapping, and will just treat it as guest memory. If this overlaps with a
memslot, we'll never be able to fault that page in, ending up with
interesting memory corruption... :-/

That's one of the reasons why I think option (2) in your earlier email
is an interesting one, as it sidesteps a whole lot of ugly and hard to
test corner cases.

Thanks,

	M.
-- 
Jazz is not dead, it just smells funny...
_______________________________________________
kvmarm mailing list
kvmarm@lists.cs.columbia.edu
https://lists.cs.columbia.edu/mailman/listinfo/kvmarm

  reply index

Thread overview: 45+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-08-02 14:50 [PATCH 0/9] arm64: Stolen time support Steven Price
2019-08-02 14:50 ` [PATCH 1/9] KVM: arm64: Document PV-time interface Steven Price
2019-08-03 11:13   ` Marc Zyngier
2019-08-05 13:06     ` Steven Price
2019-08-05  3:23   ` Zenghui Yu
2019-08-05 13:06     ` Steven Price
2019-08-05 16:40   ` Christophe de Dinechin
2019-08-07 13:21     ` Steven Price
2019-08-07 14:28       ` Christophe de Dinechin
2019-08-07 15:26         ` Steven Price
2019-08-02 14:50 ` [PATCH 2/9] KVM: arm/arm64: Factor out hypercall handling from PSCI code Steven Price
2019-08-02 14:50 ` [PATCH 3/9] KVM: arm64: Implement PV_FEATURES call Steven Price
2019-08-03 11:21   ` Marc Zyngier
2019-08-05 13:14     ` Steven Price
2019-08-02 14:50 ` [PATCH 4/9] KVM: arm64: Support stolen time reporting via shared structure Steven Price
2019-08-03 11:55   ` Marc Zyngier
2019-08-05 14:09     ` Steven Price
2019-08-03 17:58   ` Marc Zyngier
2019-08-03 18:13     ` Marc Zyngier
2019-08-05 14:18       ` Steven Price
2019-08-02 14:50 ` [PATCH 5/9] KVM: Allow kvm_device_ops to be const Steven Price
2019-08-02 14:50 ` [PATCH 6/9] KVM: arm64: Provide a PV_TIME device to user space Steven Price
2019-08-03 12:51   ` Marc Zyngier
2019-08-03 17:34     ` Marc Zyngier
2019-08-07 13:39       ` Steven Price
2019-08-07 13:51         ` Marc Zyngier
2019-08-05 16:10     ` Steven Price
2019-08-05 16:28       ` Marc Zyngier [this message]
2019-08-02 14:50 ` [PATCH 7/9] arm/arm64: Provide a wrapper for SMCCC 1.1 calls Steven Price
2019-08-05 10:03   ` Will Deacon
2019-08-02 14:50 ` [PATCH 8/9] arm/arm64: Make use of the SMCCC 1.1 wrapper Steven Price
2019-08-02 14:50 ` [PATCH 9/9] arm64: Retrieve stolen time as paravirtualized guest Steven Price
2019-08-04  9:53   ` Marc Zyngier
2019-08-08 15:29     ` Steven Price
2019-08-08 15:49       ` Marc Zyngier
2019-08-09 13:51   ` Zenghui Yu
2019-08-12 10:39     ` Steven Price
2019-08-13  6:06       ` Zenghui Yu
2019-08-03 18:05 ` [PATCH 0/9] arm64: Stolen time support Marc Zyngier
2019-08-05 13:06   ` Steven Price
2019-08-05 13:26     ` Marc Zyngier
2019-08-14 13:02     ` Alexander Graf
2019-08-14 14:19       ` Marc Zyngier
2019-08-14 14:52         ` [UNVERIFIED SENDER] " Alexander Graf
2019-08-16 10:23           ` Steven Price

Reply instructions:

You may reply publically 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=c18f9d74-48eb-3e03-dca8-ad44e6d6b682@kernel.org \
    --to=maz@kernel.org \
    --cc=catalin.marinas@arm.com \
    --cc=kvm@vger.kernel.org \
    --cc=kvmarm@lists.cs.columbia.edu \
    --cc=linux-arm-kernel@lists.infradead.org \
    --cc=linux-doc@vger.kernel.org \
    --cc=linux-kernel@vger.kernel.org \
    --cc=linux@armlinux.org.uk \
    --cc=pbonzini@redhat.com \
    --cc=steven.price@arm.com \
    --cc=will@kernel.org \
    /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

KVM ARM Archive on lore.kernel.org

Archives are clonable:
	git clone --mirror https://lore.kernel.org/kvmarm/0 kvmarm/git/0.git

	# If you have public-inbox 1.1+ installed, you may
	# initialize and index your mirror using the following commands:
	public-inbox-init -V2 kvmarm kvmarm/ https://lore.kernel.org/kvmarm \
		kvmarm@lists.cs.columbia.edu kvmarm@archiver.kernel.org
	public-inbox-index kvmarm


Newsgroup available over NNTP:
	nntp://nntp.lore.kernel.org/edu.columbia.cs.lists.kvmarm


AGPL code for this site: git clone https://public-inbox.org/ public-inbox