From: Steven Price <steven.price@arm.com>
To: Catalin Marinas <catalin.marinas@arm.com>
Cc: Marc Zyngier <maz@kernel.org>, Will Deacon <will@kernel.org>,
James Morse <james.morse@arm.com>,
Julien Thierry <julien.thierry.kdev@gmail.com>,
Suzuki K Poulose <suzuki.poulose@arm.com>,
kvmarm@lists.cs.columbia.edu,
linux-arm-kernel@lists.infradead.org,
linux-kernel@vger.kernel.org, Dave Martin <Dave.Martin@arm.com>,
Mark Rutland <mark.rutland@arm.com>,
Thomas Gleixner <tglx@linutronix.de>,
qemu-devel@nongnu.org, Juan Quintela <quintela@redhat.com>,
"Dr. David Alan Gilbert" <dgilbert@redhat.com>,
Richard Henderson <richard.henderson@linaro.org>,
Peter Maydell <peter.maydell@linaro.org>,
Haibo Xu <Haibo.Xu@arm.com>, Andrew Jones <drjones@redhat.com>
Subject: Re: [PATCH v12 7/8] KVM: arm64: ioctl to fetch/store tags in a guest
Date: Thu, 20 May 2021 16:58:01 +0100 [thread overview]
Message-ID: <dd5ab3a0-5a74-b145-2485-d6d871be945b@arm.com> (raw)
In-Reply-To: <20210520120556.GC12251@arm.com>
On 20/05/2021 13:05, Catalin Marinas wrote:
> On Mon, May 17, 2021 at 01:32:38PM +0100, Steven Price wrote:
>> diff --git a/arch/arm64/include/uapi/asm/kvm.h b/arch/arm64/include/uapi/asm/kvm.h
>> index 24223adae150..b3edde68bc3e 100644
>> --- a/arch/arm64/include/uapi/asm/kvm.h
>> +++ b/arch/arm64/include/uapi/asm/kvm.h
>> @@ -184,6 +184,17 @@ struct kvm_vcpu_events {
>> __u32 reserved[12];
>> };
>>
>> +struct kvm_arm_copy_mte_tags {
>> + __u64 guest_ipa;
>> + __u64 length;
>> + void __user *addr;
>> + __u64 flags;
>> + __u64 reserved[2];
>
> I forgot the past discussions, what's the reserved for? Future
> expansion?
Yes - for future expansion. Marc asked for them[1]:
> I'd be keen on a couple of reserved __64s. Just in case...
[1] https://lore.kernel.org/r/87ft14xl9e.wl-maz%40kernel.org
>> diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c
>> index e89a5e275e25..4b6c83beb75d 100644
>> --- a/arch/arm64/kvm/arm.c
>> +++ b/arch/arm64/kvm/arm.c
>> @@ -1309,6 +1309,65 @@ static int kvm_vm_ioctl_set_device_addr(struct kvm *kvm,
>> }
>> }
>>
>> +static int kvm_vm_ioctl_mte_copy_tags(struct kvm *kvm,
>> + struct kvm_arm_copy_mte_tags *copy_tags)
>> +{
>> + gpa_t guest_ipa = copy_tags->guest_ipa;
>> + size_t length = copy_tags->length;
>> + void __user *tags = copy_tags->addr;
>> + gpa_t gfn;
>> + bool write = !(copy_tags->flags & KVM_ARM_TAGS_FROM_GUEST);
>> + int ret = 0;
>> +
>> + if (copy_tags->reserved[0] || copy_tags->reserved[1])
>> + return -EINVAL;
>> +
>> + if (copy_tags->flags & ~KVM_ARM_TAGS_FROM_GUEST)
>> + return -EINVAL;
>> +
>> + if (length & ~PAGE_MASK || guest_ipa & ~PAGE_MASK)
>> + return -EINVAL;
>> +
>> + gfn = gpa_to_gfn(guest_ipa);
>> +
>> + mutex_lock(&kvm->slots_lock);
>> +
>> + while (length > 0) {
>> + kvm_pfn_t pfn = gfn_to_pfn_prot(kvm, gfn, write, NULL);
>> + void *maddr;
>> + unsigned long num_tags = PAGE_SIZE / MTE_GRANULE_SIZE;
>> +
>> + if (is_error_noslot_pfn(pfn)) {
>> + ret = -EFAULT;
>> + goto out;
>> + }
>> +
>> + maddr = page_address(pfn_to_page(pfn));
>> +
>> + if (!write) {
>> + num_tags = mte_copy_tags_to_user(tags, maddr, num_tags);
>> + kvm_release_pfn_clean(pfn);
>
> Do we need to check if PG_mte_tagged is set? If the page was not faulted
> into the guest address space but the VMM has the page, does the
> gfn_to_pfn_prot() guarantee that a kvm_set_spte_gfn() was called? If
> not, this may read stale tags.
Ah, I hadn't thought about that... No I don't believe gfn_to_pfn_prot()
will fault it into the guest.
>> + } else {
>> + num_tags = mte_copy_tags_from_user(maddr, tags,
>> + num_tags);
>> + kvm_release_pfn_dirty(pfn);
>> + }
>
> Same question here, if the we can't guarantee the stage 2 pte being set,
> we'd need to set PG_mte_tagged.
This is arguably worse as we'll be writing tags into the guest but
without setting PG_mte_tagged - so they'll be lost when the guest then
faults the pages in. Which sounds like it should break migration.
I think the below should be safe, and avoids the overhead of setting the
flag just for reads.
Thanks,
Steve
----8<----
page = pfn_to_page(pfn);
maddr = page_address(page);
if (!write) {
if (test_bit(PG_mte_tagged, &page->flags))
num_tags = mte_copy_tags_to_user(tags, maddr,
MTE_GRANULES_PER_PAGE);
else
/* No tags in memory, so write zeros */
num_tags = MTE_GRANULES_PER_PAGE -
clear_user(tag, MTE_GRANULES_PER_PAGE);
kvm_release_pfn_clean(pfn);
} else {
num_tags = mte_copy_tags_from_user(maddr, tags,
MTE_GRANULES_PER_PAGE);
kvm_release_pfn_dirty(pfn);
}
if (num_tags != MTE_GRANULES_PER_PAGE) {
ret = -EFAULT;
goto out;
}
if (write)
test_and_set_bit(PG_mte_tagged, &page->flags);
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next prev parent reply other threads:[~2021-05-20 15:59 UTC|newest]
Thread overview: 49+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-05-17 12:32 [PATCH v12 0/8] MTE support for KVM guest Steven Price
2021-05-17 12:32 ` [PATCH v12 1/8] arm64: mte: Handle race when synchronising tags Steven Price
2021-05-17 14:03 ` Marc Zyngier
2021-05-17 14:56 ` Steven Price
2021-05-19 17:32 ` Catalin Marinas
2021-05-17 12:32 ` [PATCH v12 2/8] arm64: Handle MTE tags zeroing in __alloc_zeroed_user_highpage() Steven Price
2021-05-17 12:32 ` [PATCH v12 3/8] arm64: mte: Sync tags for pages where PTE is untagged Steven Price
2021-05-17 16:14 ` Marc Zyngier
2021-05-19 9:32 ` Steven Price
2021-05-19 17:48 ` Catalin Marinas
2021-05-19 18:06 ` Catalin Marinas
2021-05-20 11:55 ` Steven Price
2021-05-20 12:25 ` Catalin Marinas
2021-05-20 13:02 ` Catalin Marinas
2021-05-20 13:03 ` Steven Price
2021-05-17 12:32 ` [PATCH v12 4/8] arm64: kvm: Introduce MTE VM feature Steven Price
2021-05-17 16:45 ` Marc Zyngier
2021-05-19 10:48 ` Steven Price
2021-05-20 8:51 ` Marc Zyngier
2021-05-20 14:46 ` Steven Price
2021-05-20 11:54 ` Catalin Marinas
2021-05-20 15:05 ` Steven Price
2021-05-20 17:50 ` Catalin Marinas
2021-05-21 9:28 ` Steven Price
2021-05-17 12:32 ` [PATCH v12 5/8] arm64: kvm: Save/restore MTE registers Steven Price
2021-05-17 17:17 ` Marc Zyngier
2021-05-19 13:04 ` Steven Price
2021-05-20 9:46 ` Marc Zyngier
2021-05-20 15:21 ` Steven Price
2021-05-17 12:32 ` [PATCH v12 6/8] arm64: kvm: Expose KVM_ARM_CAP_MTE Steven Price
2021-05-17 17:40 ` Marc Zyngier
2021-05-19 13:26 ` Steven Price
2021-05-20 10:09 ` Marc Zyngier
2021-05-20 10:51 ` Steven Price
2021-05-17 12:32 ` [PATCH v12 7/8] KVM: arm64: ioctl to fetch/store tags in a guest Steven Price
2021-05-17 18:04 ` Marc Zyngier
2021-05-19 13:51 ` Steven Price
2021-05-20 12:05 ` Catalin Marinas
2021-05-20 15:58 ` Steven Price [this message]
2021-05-20 17:27 ` Catalin Marinas
2021-05-21 9:42 ` Steven Price
2021-05-24 18:11 ` Catalin Marinas
2021-05-27 7:50 ` Steven Price
2021-05-27 13:08 ` Catalin Marinas
2021-05-17 12:32 ` [PATCH v12 8/8] KVM: arm64: Document MTE capability and ioctl Steven Price
2021-05-17 18:09 ` Marc Zyngier
2021-05-19 14:09 ` Steven Price
2021-05-20 10:24 ` Marc Zyngier
2021-05-20 10:52 ` Steven Price
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