From: Paul Durrant <xadimgnik@gmail.com>
To: Sean Christopherson <seanjc@google.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>,
Jonathan Corbet <corbet@lwn.net>,
Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
Dave Hansen <dave.hansen@linux.intel.com>,
x86@kernel.org, "H. Peter Anvin" <hpa@zytor.com>,
David Woodhouse <dwmw2@infradead.org>,
Shuah Khan <shuah@kernel.org>,
kvm@vger.kernel.org, linux-doc@vger.kernel.org,
linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org,
Christian Borntraeger <borntraeger@linux.ibm.com>,
Janosch Frank <frankja@linux.ibm.com>,
Claudio Imbrenda <imbrenda@linux.ibm.com>,
David Hildenbrand <david@redhat.com>
Subject: Re: [PATCH v12 08/20] KVM: pfncache: allow a cache to be activated with a fixed (userspace) HVA
Date: Wed, 14 Feb 2024 15:21:05 +0000 [thread overview]
Message-ID: <9c542f39-959e-4ab1-94a5-39e049a30743@xen.org> (raw)
In-Reply-To: <ZcMBDP6H5PRo5C2d@google.com>
On 07/02/2024 04:03, Sean Christopherson wrote:
> +s390 folks (question on kvm_is_error_gpa() for ya)
>
> On Mon, Jan 15, 2024, Paul Durrant wrote:
>> @@ -1398,7 +1414,9 @@ void kvm_gpc_deactivate(struct gfn_to_pfn_cache *gpc);
>> static inline void kvm_gpc_mark_dirty(struct gfn_to_pfn_cache *gpc)
>> {
>> lockdep_assert_held(&gpc->lock);
>> - mark_page_dirty_in_slot(gpc->kvm, gpc->memslot, gpc->gpa >> PAGE_SHIFT);
>> +
>> + if (gpc->gpa != KVM_XEN_INVALID_GPA)
>
> KVM_XEN_INVALID_GPA absolutely doesn't belong in common code. Not to mention
> that it will break when Paolo (rightly) moves it to an x86 header.
>
> https://lore.kernel.org/all/20240131233056.10845-3-pbonzini@redhat.com
>
>> + mark_page_dirty_in_slot(gpc->kvm, gpc->memslot, gpc->gpa >> PAGE_SHIFT);
>> }
>>
>> void kvm_sigset_activate(struct kvm_vcpu *vcpu);
>> diff --git a/virt/kvm/pfncache.c b/virt/kvm/pfncache.c
>> index 97eec8ee3449..ae822bff812f 100644
>> --- a/virt/kvm/pfncache.c
>> +++ b/virt/kvm/pfncache.c
>> @@ -48,7 +48,10 @@ bool kvm_gpc_check(struct gfn_to_pfn_cache *gpc, unsigned long len)
>> if (!gpc->active)
>> return false;
>>
>> - if (gpc->generation != slots->generation || kvm_is_error_hva(gpc->uhva))
>> + if (gpc->gpa != KVM_XEN_INVALID_GPA && gpc->generation != slots->generation)
>
> This needs a comment. I know what it's doing, but it wasn't obvious at first
> glance, and it definitely won't be intuitive for readers that aren't intimately
> familiar with memslots.
>
>> + return false;
>> +
>> + if (kvm_is_error_hva(gpc->uhva))
>> return false;
>>
>> if (offset_in_page(gpc->uhva) + len > PAGE_SIZE)
>> @@ -209,11 +212,13 @@ static kvm_pfn_t hva_to_pfn_retry(struct gfn_to_pfn_cache *gpc)
>> return -EFAULT;
>> }
>>
>> -static int __kvm_gpc_refresh(struct gfn_to_pfn_cache *gpc, gpa_t gpa,
>> +static int __kvm_gpc_refresh(struct gfn_to_pfn_cache *gpc, gpa_t gpa, unsigned long uhva,
>> unsigned long len)
>> {
>> struct kvm_memslots *slots = kvm_memslots(gpc->kvm);
>> - unsigned long page_offset = offset_in_page(gpa);
>> + unsigned long page_offset = (gpa != KVM_XEN_INVALID_GPA) ?
>> + offset_in_page(gpa) :
>> + offset_in_page(uhva);
>
> This formatting is funky. I also think it would be worth adding a helper to pair
> with kvm_is_error_hva().
>
> But! kvm_is_error_gpa() already exists, and it very, very sneakily does a memslot
> lookup and checks for a valid HVA.
>
> s390 people, any objection to renaming kvm_is_error_gpa() to something like
> kvm_gpa_has_memslot() or kvm_gpa_is_in_memslot()? s390 is the only code that
> uses the existing helper.
>
> That would both to free up the name to pair with kvm_is_error_hva(), and would
> make it obvious what the helper does; I was quite surprised that "error" means
> "is covered by a valid memslot".
>
Seemingly no response to this; I'll define a local helper rather than
re-working the open-coded tests to check against INVALID_GPA. This can
then be trivially replaced if need be.
> Back to this code, then we can have a slightly cleaner:
>
> unsigned long page_offset = kvm_is_error_gpa(gpa) ? offset_in_page(gpa) :
> offset_in_page(uhva);
>
>
> And I think it's worth asserting that exactly _one_ of GPA or HVA is valid, e.g.
> to ensure KVM doesn't end up with botched offsets, and to make it a bit more
> clear what's going on.
>
>
> if (WARN_ON_ONCE(kvm_is_error_gpa(gpa) == kvm_is_error_hva(uhva))
> return -EINVAL;
Sure.
next prev parent reply other threads:[~2024-02-14 15:21 UTC|newest]
Thread overview: 58+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-01-15 12:56 [PATCH v12 00/20] KVM: xen: update shared_info and vcpu_info handling Paul Durrant
2024-01-15 12:56 ` [PATCH v12 01/20] KVM: pfncache: Add a map helper function Paul Durrant
2024-01-15 12:56 ` [PATCH v12 02/20] KVM: pfncache: remove unnecessary exports Paul Durrant
2024-01-15 12:56 ` [PATCH v12 03/20] KVM: xen: mark guest pages dirty with the pfncache lock held Paul Durrant
2024-02-07 3:17 ` Sean Christopherson
2024-02-07 3:26 ` David Woodhouse
2024-02-07 15:15 ` Sean Christopherson
2024-02-07 8:48 ` Paul Durrant
2024-01-15 12:56 ` [PATCH v12 04/20] KVM: pfncache: add a mark-dirty helper Paul Durrant
2024-02-07 3:20 ` Sean Christopherson
2024-02-07 8:47 ` Paul Durrant
2024-02-09 15:58 ` Sean Christopherson
2024-02-09 16:05 ` Paul Durrant
2024-01-15 12:56 ` [PATCH v12 05/20] KVM: pfncache: remove KVM_GUEST_USES_PFN usage Paul Durrant
2024-01-15 12:56 ` [PATCH v12 06/20] KVM: pfncache: stop open-coding offset_in_page() Paul Durrant
2024-01-15 12:56 ` [PATCH v12 07/20] KVM: pfncache: include page offset in uhva and use it consistently Paul Durrant
2024-01-15 12:56 ` [PATCH v12 08/20] KVM: pfncache: allow a cache to be activated with a fixed (userspace) HVA Paul Durrant
2024-02-07 4:03 ` Sean Christopherson
2024-02-07 4:13 ` David Woodhouse
2024-02-14 16:01 ` Sean Christopherson
2024-02-14 16:09 ` Paul Durrant
2024-02-14 15:21 ` Paul Durrant [this message]
2024-02-14 16:20 ` Sean Christopherson
2024-02-14 16:33 ` Paul Durrant
2024-01-15 12:56 ` [PATCH v12 09/20] KVM: xen: separate initialization of shared_info cache and content Paul Durrant
2024-01-15 12:56 ` [PATCH v12 10/20] KVM: xen: re-initialize shared_info if guest (32/64-bit) mode is set Paul Durrant
2024-01-15 12:56 ` [PATCH v12 11/20] KVM: xen: allow shared_info to be mapped by fixed HVA Paul Durrant
2024-02-07 4:10 ` Sean Christopherson
2024-02-07 8:53 ` Paul Durrant
2024-02-08 8:52 ` Paul Durrant
2024-02-08 16:48 ` Sean Christopherson
2024-02-08 16:51 ` Paul Durrant
2024-02-08 17:26 ` David Woodhouse
2024-02-09 16:01 ` Sean Christopherson
2024-01-15 12:56 ` [PATCH v12 12/20] KVM: xen: allow vcpu_info " Paul Durrant
2024-01-15 12:57 ` [PATCH v12 13/20] KVM: selftests / xen: map shared_info using HVA rather than GFN Paul Durrant
2024-02-07 4:14 ` Sean Christopherson
2024-02-07 8:54 ` Paul Durrant
2024-02-07 14:58 ` Sean Christopherson
2024-01-15 12:57 ` [PATCH v12 14/20] KVM: selftests / xen: re-map vcpu_info using HVA rather than GPA Paul Durrant
2024-01-15 12:57 ` [PATCH v12 15/20] KVM: xen: advertize the KVM_XEN_HVM_CONFIG_SHARED_INFO_HVA capability Paul Durrant
2024-01-15 12:57 ` [PATCH v12 16/20] KVM: xen: split up kvm_xen_set_evtchn_fast() Paul Durrant
2024-01-15 12:57 ` [PATCH v12 17/20] KVM: xen: don't block on pfncache locks in kvm_xen_set_evtchn_fast() Paul Durrant
2024-02-07 4:17 ` Sean Christopherson
2024-02-07 4:21 ` David Woodhouse
2024-01-15 12:57 ` [PATCH v12 18/20] KVM: pfncache: check the need for invalidation under read lock first Paul Durrant
2024-02-07 4:22 ` Sean Christopherson
2024-02-07 4:27 ` David Woodhouse
2024-02-07 4:47 ` Sean Christopherson
2024-02-07 4:59 ` David Woodhouse
2024-02-07 15:10 ` Sean Christopherson
2024-01-15 12:57 ` [PATCH v12 19/20] KVM: xen: allow vcpu_info content to be 'safely' copied Paul Durrant
2024-01-15 12:57 ` [PATCH v12 20/20] KVM: pfncache: rework __kvm_gpc_refresh() to fix locking issues Paul Durrant
2024-01-25 15:03 ` [PATCH v12 00/20] KVM: xen: update shared_info and vcpu_info handling Paul Durrant
2024-01-25 20:07 ` David Woodhouse
2024-01-26 1:19 ` Sean Christopherson
2024-02-02 17:37 ` Paul Durrant
2024-02-02 22:03 ` Sean Christopherson
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