From: Sean Christopherson <seanjc@google.com>
To: Ricardo Koller <ricarkol@google.com>
Cc: kvm@vger.kernel.org, kvmarm@lists.cs.columbia.edu,
andrew.jones@linux.dev, pbonzini@redhat.com, maz@kernel.org,
alexandru.elisei@arm.com, eric.auger@redhat.com,
oupton@google.com, reijiw@google.com, rananta@google.com,
bgardon@google.com, dmatlack@google.com,
axelrasmussen@google.com, Oliver Upton <oliver.upton@linux.dev>
Subject: Re: [PATCH v7 08/13] KVM: selftests: Use the right memslot for code, page-tables, and data allocations
Date: Tue, 20 Sep 2022 18:40:03 +0000 [thread overview]
Message-ID: <YyoJA7gjEaSiGwFi@google.com> (raw)
In-Reply-To: <YyoFBBn9uevAkIHT@google.com>
On Tue, Sep 20, 2022, Ricardo Koller wrote:
> On Tue, Sep 20, 2022 at 06:07:13PM +0000, Sean Christopherson wrote:
> > On Tue, Sep 20, 2022, Ricardo Koller wrote:
> > > The previous commit added support for callers of ____vm_create() to specify
> >
> > Changelog is stale, ____vm_create() no longer takes the struct.
> >
> > Side topic, it's usually a good idea to use "strong" terminology when referencing
> > past/future changes, e.g. if patches get shuffled around for whatever reason,
> > then "previous commit" may become stale/misleading.
> >
> > It's fairly easy to convey the same info ("something happened recently" or
> > "something is going to happen soon") without being so explicit, e.g.
> >
> > Wire up common code to use the appropriate code, page table, and data
> > memmslots that were recently added instead of hardcoding '0' for the
> > memslot.
> >
> > or
> >
> > Now that kvm_vm allows specifying different memslots for code, page
> > tables, and data, use the appropriate memslot when making allocations
> > in common/libraty code.
> >
> > > what memslots to use for code, page-tables, and data allocations. Change
> > > them accordingly:
> > >
> > > - stacks, code, and exception tables use the code memslot
> >
> > Huh? Stacks and exceptions are very much data, not code.
> >
>
> I would *really* like to have the data region only store test data. It
> makes things easier for the test implementation, like owning the whole
> region.
That's fine, but allocating stack as "code" is super confusing.
> At the same I wanted to have a single region for all the "core pages" like
> code, descriptors, exception tables, stacks, etc. Not sure what to call it
> though.
Why? Code is very different than all those other things. E.g. the main reason
KVM doesn't provide "not-executable" or "execute-only" memslots is because there's
never been a compelling use case, not because it's difficult to implement. If KVM
were to ever add such functionality, then we'd want/need selftests to have a
dedicated code memslot.
> So, what about one of these 2 options:
>
> Option A: 3 regions, where we call the "code" region something else, like
> "core".
> Option B: 4 regions: code, page-tables, core-data (stacks, exception tables, etc),
> test-data.
I like (B), though I'd just call 'em "DATA" and "TEST_DATA". IIUC, TEST_DATA is
the one you want to be special, i.e. it's ok if something that's not "core" allocates
in DATA, but it's not ok if "core" allocates in TEST_DATA. That yields an easy
to understand "never use TEST_DATA" rule for library/common/core functionality,
with the code vs. page tables vs. data decision (hopefully) being fairly obvious.
Defining CORE_DATA will force developers to make judgement calls and probably
lead to bikeshedding over whether something is considered "core" code.
next prev parent reply other threads:[~2022-09-20 18:40 UTC|newest]
Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-09-20 4:25 [PATCH v7 00/13] KVM: selftests: Add aarch64/page_fault_test Ricardo Koller
2022-09-20 4:25 ` [PATCH v7 01/13] KVM: selftests: Add a userfaultfd library Ricardo Koller
2022-09-20 4:25 ` [PATCH v7 02/13] KVM: selftests: aarch64: Add virt_get_pte_hva() library function Ricardo Koller
2022-09-20 4:25 ` [PATCH v7 03/13] KVM: selftests: Add missing close and munmap in __vm_mem_region_delete() Ricardo Koller
2022-09-20 4:25 ` [PATCH v7 04/13] KVM: selftests: aarch64: Construct DEFAULT_MAIR_EL1 using sysreg.h macros Ricardo Koller
2022-09-20 4:25 ` [PATCH v7 05/13] tools: Copy bitfield.h from the kernel sources Ricardo Koller
2022-09-20 4:25 ` [PATCH v7 06/13] KVM: selftests: Stash backing_src_type in struct userspace_mem_region Ricardo Koller
2022-09-20 4:25 ` [PATCH v7 07/13] KVM: selftests: Add vm->memslots[] and enum kvm_mem_region_type Ricardo Koller
2022-09-20 7:50 ` Andrew Jones
2022-09-20 17:39 ` Sean Christopherson
2022-09-20 17:49 ` Ricardo Koller
2022-09-20 4:25 ` [PATCH v7 08/13] KVM: selftests: Use the right memslot for code, page-tables, and data allocations Ricardo Koller
2022-09-20 7:51 ` Andrew Jones
2022-09-20 18:07 ` Sean Christopherson
2022-09-20 18:23 ` Ricardo Koller
2022-09-20 18:40 ` Sean Christopherson [this message]
2022-09-20 18:57 ` Ricardo Koller
2022-09-20 4:25 ` [PATCH v7 09/13] KVM: selftests: aarch64: Add aarch64/page_fault_test Ricardo Koller
2022-09-20 8:05 ` Andrew Jones
2022-09-20 17:13 ` Ricardo Koller
2022-09-20 4:25 ` [PATCH v7 10/13] KVM: selftests: aarch64: Add userfaultfd tests into page_fault_test Ricardo Koller
2022-09-20 4:25 ` [PATCH v7 11/13] KVM: selftests: aarch64: Add dirty logging " Ricardo Koller
2022-09-20 4:25 ` [PATCH v7 12/13] KVM: selftests: aarch64: Add readonly memslot " Ricardo Koller
2022-09-20 4:25 ` [PATCH v7 13/13] KVM: selftests: aarch64: Add mix of " Ricardo Koller
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