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From: Oliver Upton <oliver.upton@linux.dev>
To: Ricardo Koller <ricarkol@google.com>
Cc: kvm@vger.kernel.org, kvmarm@lists.linux.dev, andrew.jones@linux.dev,
	pbonzini@redhat.com, maz@kernel.org, alexandru.elisei@arm.com,
	eric.auger@redhat.com, yuzenghui@huawei.com
Subject: Re: [PATCH 1/4] KVM: selftests: aarch64: Relax userfaultfd read vs.
 write checks
Message-ID: <Y88TLcuetXMSYyfD@google.com>
References: <20230110022432.330151-1-ricarkol@google.com>
 <20230110022432.330151-2-ricarkol@google.com>
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On Tue, Jan 10, 2023 at 02:24:29AM +0000, Ricardo Koller wrote:
> Only Stage1 Page table walks (S1PTW) writing a PTE on an unmapped page
> should result in a userfaultfd write. However, the userfaultfd tests in
> page_fault_test wrongly assert that any S1PTW is a PTE write.
> 
> Fix this by relaxing the read vs. write checks in all userfaultfd handlers.
> Note that this is also an attempt to focus less on KVM (and userfaultfd)
> behavior, and more on architectural behavior. Also note that after commit
> "KVM: arm64: Fix S1PTW handling on RO memslots" the userfaultfd fault
> (S1PTW with AF on an unmaped PTE page) is actually a read: the translation
> fault that comes before the permission fault.

I certainly agree that we cannot make assertions about read v. write
when registering uffd in 'missing' mode. We probably need another test
to assert that we get write faults for hardware AF updates when using
uffd in write protect mode.

--
Thanks,
Oliver