* [PATCH v9 1/9] tracing/probes: Allow eprobe to use variable without $ prefix
From: Masami Hiramatsu (Google) @ 2026-06-25 1:25 UTC (permalink / raw)
To: Steven Rostedt, Mathieu Desnoyers
Cc: Jonathan Corbet, Shuah Khan, Masami Hiramatsu, linux-kernel,
linux-trace-kernel, linux-doc, linux-kselftest
In-Reply-To: <178235074943.766912.25308838431649508.stgit@devnote2>
From: Masami Hiramatsu (Google) <mhiramat@kernel.org>
The commit 69efd863a785 ("tracing/eprobes: Allow use of BTF names
to dereference pointers") allows eprobe to use event field without
"$" prefix when it is used with typecast, it is natual to allow it
without typecast.
Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
---
Changes in v8:
- Newly added.
---
kernel/trace/trace_probe.c | 12 +++++++++++-
kernel/trace/trace_probe.h | 1 +
.../test.d/dynevent/eprobes_syntax_errors.tc | 3 +--
3 files changed, 13 insertions(+), 3 deletions(-)
diff --git a/kernel/trace/trace_probe.c b/kernel/trace/trace_probe.c
index 0da7c0b53ba7..2ce7d62471cb 100644
--- a/kernel/trace/trace_probe.c
+++ b/kernel/trace/trace_probe.c
@@ -1341,7 +1341,17 @@ parse_probe_arg(char *arg, const struct fetch_type *type,
ret = handle_typecast(arg, pcode, end, ctx);
break;
default:
- if (isalpha(arg[0]) || arg[0] == '_') { /* BTF variable */
+ if (isalpha(arg[0]) || arg[0] == '_') {
+ /* BTF variable or event field*/
+ if (ctx->flags & TPARG_FL_TEVENT) {
+ ret = parse_trace_event(arg, *pcode, ctx);
+ if (ret < 0) {
+ trace_probe_log_err(ctx->offset,
+ NO_EVENT_FIELD);
+ return -EINVAL;
+ }
+ break;
+ }
if (!tparg_is_function_entry(ctx->flags) &&
!tparg_is_function_return(ctx->flags)) {
trace_probe_log_err(ctx->offset, NOSUP_BTFARG);
diff --git a/kernel/trace/trace_probe.h b/kernel/trace/trace_probe.h
index 40b53b5b58a9..2e0d8384ee5c 100644
--- a/kernel/trace/trace_probe.h
+++ b/kernel/trace/trace_probe.h
@@ -559,6 +559,7 @@ extern int traceprobe_define_arg_fields(struct trace_event_call *event_call,
C(NO_PTR_STRCT, "This is not a pointer to union/structure."), \
C(NOSUP_DAT_ARG, "Non pointer structure/union argument is not supported."),\
C(BAD_HYPHEN, "Failed to parse single hyphen. Forgot '>'?"), \
+ C(NO_EVENT_FIELD, "This event field is not found."), \
C(NO_BTF_FIELD, "This field is not found."), \
C(BAD_BTF_TID, "Failed to get BTF type info."),\
C(BAD_TYPE4STR, "This type does not fit for string."),\
diff --git a/tools/testing/selftests/ftrace/test.d/dynevent/eprobes_syntax_errors.tc b/tools/testing/selftests/ftrace/test.d/dynevent/eprobes_syntax_errors.tc
index 2a680c086047..0e65e787e426 100644
--- a/tools/testing/selftests/ftrace/test.d/dynevent/eprobes_syntax_errors.tc
+++ b/tools/testing/selftests/ftrace/test.d/dynevent/eprobes_syntax_errors.tc
@@ -10,7 +10,7 @@ check_error() { # command-with-error-pos-by-^
check_error 'e ^a.' # NO_EVENT_INFO
check_error 'e ^.b' # NO_EVENT_INFO
check_error 'e ^a.b' # BAD_ATTACH_EVENT
-check_error 'e syscalls/sys_enter_openat ^foo' # BAD_ATTACH_ARG
+check_error 'e syscalls/sys_enter_openat ^foo' # NO_EVENT_FIELD
check_error 'e:^/bar syscalls/sys_enter_openat' # NO_GROUP_NAME
check_error 'e:^12345678901234567890123456789012345678901234567890123456789012345/bar syscalls/sys_enter_openat' # GROUP_TOO_LONG
@@ -19,7 +19,6 @@ check_error 'e:^ syscalls/sys_enter_openat' # NO_EVENT_NAME
check_error 'e:foo/^12345678901234567890123456789012345678901234567890123456789012345 syscalls/sys_enter_openat' # EVENT_TOO_LONG
check_error 'e:foo/^bar.1 syscalls/sys_enter_openat' # BAD_EVENT_NAME
-check_error 'e:foo/bar syscalls/sys_enter_openat arg=^dfd' # BAD_FETCH_ARG
check_error 'e:foo/bar syscalls/sys_enter_openat arg=^$foo' # BAD_ATTACH_ARG
if grep -q '<attached-group>\.<attached-event>.*\[if <filter>\]' README; then
^ permalink raw reply related
* [PATCH v9 0/9] tracing/probes: Add more typecast features
From: Masami Hiramatsu (Google) @ 2026-06-25 1:25 UTC (permalink / raw)
To: Steven Rostedt, Mathieu Desnoyers
Cc: Jonathan Corbet, Shuah Khan, Masami Hiramatsu, linux-kernel,
linux-trace-kernel, linux-doc, linux-kselftest
Hi,
Here is the 9th version of series to introduce more typecast features
to probe events. The previous version is here:
https://lore.kernel.org/all/178231208703.732967.1160700962651040729.stgit@devnote2/
In this version, I removed picked bugfix patch, prohibit percpu
access method on non-kernel probes [8/9], and add a test case
to check the new syntax[9/9].
This series extends BTF typecast feature and add more options:
1. Expanding BTF typecast to kprobe and fprobe.
(currently only function entry/exit)
2. Introduce container_of like typecast. This adds a "assigned
member" option to the typecast.
(STRUCT,MEMBER)VAR->ANOTHER_MEMBER
This casts VAR to STRUCT type but the VAR is as the address
of STRUCT.MEMBER. In C, it is:
container_of(VAR, STRUCT, MEMBER)->ANOTHER_MEMBER
3. Support nested typecast, e.g.
(STRUCT)((STRUCT2)VAR->MEMBER2)->MEMBER
the nest level must be smaller than 3.
4. Add $current variable to point "current" task_struct.
This is useful with typecast, e.g.
(task_struct)$current->pid
5. per-cpu dereference support.
Intrdouce this_cpu_read(VAR) and this_cpu_ptr(VAR) to
access per-cpu data on the current CPU (accessing other CPU
data is not stable, because it can be changed.)
You can access the member of per-cpu data structure using
typecast like:
(STRUCT)this_cpu_ptr(VAR)->MEMBER
6. Support event fields without $ prefix on eprobes.
Now eprobe events can access its event fields.
And added fetcharg dump feature (for debug) and updated test scripts
to test part of them.
Thanks,
---
base-commit: c69b5f959286395e94c237ce6d7d4970bad7f6e3
Masami Hiramatsu (Google) (9):
tracing/probes: Allow eprobe to use variable without $ prefix
tracing/probes: Support dumping fetcharg program for debugging dynamic events
tracing/probes: Support typecast for various probe events
tracing/probes: Support nested typecast
tracing/probes: Type casting always involves nested calls
tracing/probes: Support field specifier option for typecast
tracing/probes: Add $current variable support
tracing/probes: Add this_cpu_read() and this_cpu_ptr() dereference method to fetcharg
tracing/probes: Add a new testcase for BTF typecasts
Documentation/trace/eprobetrace.rst | 9
Documentation/trace/fprobetrace.rst | 10
Documentation/trace/kprobetrace.rst | 11
kernel/trace/Kconfig | 12
kernel/trace/trace.c | 8
kernel/trace/trace_eprobe.c | 2
kernel/trace/trace_fprobe.c | 2
kernel/trace/trace_kprobe.c | 2
kernel/trace/trace_probe.c | 579 ++++++++++++++++----
kernel/trace/trace_probe.h | 100 ++-
kernel/trace/trace_probe_tmpl.h | 25 +
kernel/trace/trace_uprobe.c | 3
samples/trace_events/trace-events-sample.c | 40 +
samples/trace_events/trace-events-sample.h | 34 +
.../ftrace/test.d/dynevent/btf_probe_event.tc | 51 ++
.../test.d/dynevent/btf_typecast_accepted.tc | 107 ++++
.../test.d/dynevent/eprobes_syntax_errors.tc | 6
.../ftrace/test.d/dynevent/fprobe_syntax_errors.tc | 12
.../ftrace/test.d/kprobe/kprobe_syntax_errors.tc | 12
.../ftrace/test.d/kprobe/uprobe_syntax_errors.tc | 5
20 files changed, 876 insertions(+), 154 deletions(-)
create mode 100644 tools/testing/selftests/ftrace/test.d/dynevent/btf_probe_event.tc
create mode 100644 tools/testing/selftests/ftrace/test.d/dynevent/btf_typecast_accepted.tc
--
Masami Hiramatsu (Google) <mhiramat@kernel.org>
^ permalink raw reply
* Re: [PATCH v8 24/46] KVM: guest_memfd: Make in-place conversion the default
From: Yan Zhao @ 2026-06-25 1:21 UTC (permalink / raw)
To: Ackerley Tng
Cc: aik, andrew.jones, binbin.wu, brauner, chao.p.peng, david,
jmattson, jthoughton, michael.roth, oupton, pankaj.gupta, qperret,
rick.p.edgecombe, rientjes, shivankg, steven.price, tabba, willy,
wyihan, forkloop, pratyush, suzuki.poulose, aneesh.kumar, liam,
Paolo Bonzini, Sean Christopherson, Thomas Gleixner, Ingo Molnar,
Borislav Petkov, Dave Hansen, x86, H. Peter Anvin, Steven Rostedt,
Masami Hiramatsu, Mathieu Desnoyers, Jonathan Corbet, Shuah Khan,
Shuah Khan, Vishal Annapurve, Andrew Morton, Chris Li,
Kairui Song, Kemeng Shi, Nhat Pham, Barry Song, Axel Rasmussen,
Yuanchu Xie, Wei Xu, Youngjun Park, Qi Zheng, Shakeel Butt,
Kiryl Shutsemau, Baoquan He, Jason Gunthorpe, Vlastimil Babka,
kvm, linux-kernel, linux-trace-kernel, linux-doc, linux-kselftest,
linux-mm, linux-coco
In-Reply-To: <CAEvNRgHYTFnHbsLLgMTCSitmnp1_j9Pomikm9qmpGTh1w8YE5Q@mail.gmail.com>
On Wed, Jun 24, 2026 at 05:05:44PM -0700, Ackerley Tng wrote:
> Yan Zhao <yan.y.zhao@intel.com> writes:
>
> >
> > [...snip...]
> >
> >>
> >> #ifdef kvm_arch_has_private_mem
> >> -bool __ro_after_init gmem_in_place_conversion = false;
> >> +bool __ro_after_init gmem_in_place_conversion = !IS_ENABLED(CONFIG_KVM_VM_MEMORY_ATTRIBUTES);
> >> +module_param(gmem_in_place_conversion, bool, 0444);
> >
> > With gmem_in_place_conversion=true, userspace can create guest_memfd without the
> > MMAP flag. In such cases, shared memory is allocated from different backends.
> > This means this module parameter only enables per-gmem memory attribute and does
> > not guarantee that gmem in-place conversion will actually occur.
> >
> > To avoid confusion, could we rename this module parameter to something more
> > accurate, such as gmem_memory_attribute?
> >
>
> I asked Sean about this after getting some fixes off list. Sean said
> gmem_in_place_conversion is named for a host admin to use, and something
> like gmem_memory_attributes is too much implementation details for the
> admin.
Thanks for this background.
Some more context on why I'm asking:
Currently, I'm testing TDX huge pages with the following two gmem components:
1. The gmem memory attribute in this gmem in-place conversion v8.
2. The gmem 2MB from buddy allocator. (for development/testing only).
The gmem 2MB from buddy allocator allocates 2MB folios from buddy for private
memory, while shared memory is allocated from a different backend.
(To avoid fragmentation, only private mappings are split during private-to-shared
conversions. In this approach, the 2MB folios are always retained in the gmem
inode filemap cache without splitting.)
Since shared memory is not allocated from gmem, there're no in-place conversions.
The reason I'm using "gmem memory attribute" is that the per-VM attribute is
being deprecated, as suggested by Sean [1].
Besides my current usage, there may be other scenarios where gmem memory
attributes is preferred without allocating shared memory from gmem.
(e.g., PAGE.ADD from a temp extra shared source memory).
For such use cases, I'm concerns that the admins may find it confusing if they
enable gmem_in_place_conversion but still observe extra memory consumptions for
shared memory.
[1] https://lore.kernel.org/kvm/aWmEegVP_A613WIr@google.com/
> Sean, would you reconsider since Yan also asked? If the admin compiled
> the kernel knowing what CONFIG_KVM_VM_MEMORY_ATTRIBUTES means, then the
> admin would also be able to use a param like gmem_memory_attributes?
>
> There's the additional benefit that the similar naming aids in
> understanding for both the admin and software engineers.
>
> Either way, in the next revision, I'll also add this documentation for
> this module_param:
>
> Setting the module parameter gmem_in_place_conversion to true will
> enable the KVM_SET_MEMORY_ATTRIBUTES2 guest_memfd ioctl and disables
> the KVM_SET_MEMORY_ATTRIBUTES VM ioctl. If gmem_in_place_conversion is
> true, the private/shared attribute will be tracked per-guest_memfd
> instead of per-VM.
>
> Let me know what y'all think of the wording!
>
> >>
> >> [...snip...]
> >>
^ permalink raw reply
* Re: [PATCH v8 24/46] KVM: guest_memfd: Make in-place conversion the default
From: Sean Christopherson @ 2026-06-25 0:41 UTC (permalink / raw)
To: Ackerley Tng
Cc: Yan Zhao, aik, andrew.jones, binbin.wu, brauner, chao.p.peng,
david, jmattson, jthoughton, michael.roth, oupton, pankaj.gupta,
qperret, rick.p.edgecombe, rientjes, shivankg, steven.price,
tabba, willy, wyihan, forkloop, pratyush, suzuki.poulose,
aneesh.kumar, liam, Paolo Bonzini, Thomas Gleixner, Ingo Molnar,
Borislav Petkov, Dave Hansen, x86, H. Peter Anvin, Steven Rostedt,
Masami Hiramatsu, Mathieu Desnoyers, Jonathan Corbet, Shuah Khan,
Shuah Khan, Vishal Annapurve, Andrew Morton, Chris Li,
Kairui Song, Kemeng Shi, Nhat Pham, Barry Song, Axel Rasmussen,
Yuanchu Xie, Wei Xu, Youngjun Park, Qi Zheng, Shakeel Butt,
Kiryl Shutsemau, Baoquan He, Jason Gunthorpe, Vlastimil Babka,
kvm, linux-kernel, linux-trace-kernel, linux-doc, linux-kselftest,
linux-mm, linux-coco
In-Reply-To: <CAEvNRgHYTFnHbsLLgMTCSitmnp1_j9Pomikm9qmpGTh1w8YE5Q@mail.gmail.com>
On Wed, Jun 24, 2026, Ackerley Tng wrote:
> Yan Zhao <yan.y.zhao@intel.com> writes:
> > With gmem_in_place_conversion=true, userspace can create guest_memfd without the
> > MMAP flag. In such cases, shared memory is allocated from different backends.
> > This means this module parameter only enables per-gmem memory attribute and does
> > not guarantee that gmem in-place conversion will actually occur.
KVM module params are pretty much always about what KVM supports, not what is
guaranteed to happen.
- enable_mmio_caching doesn't guarantee there will actually be MMIO SPTEs,
because maybe the guest never accesses emulated MMIO.
- enable_pmu doesn't guarantee VMs will get a PMU, because userspace may elect
not to advertise one.
- and so on and so forth...
Yes, there's a small mental jump to get from "KVM supports in-place conversion"
to "I need to set memory attributes on the guest_memfd instance, not the VM",
but I don't see that as a big hurdle, certainly not in the long term. And once
the VMM code is written, I really do think most people are going to care about
whether or not KVM supports in-place conversion, not where PRIVATE is tracked.
> > To avoid confusion, could we rename this module parameter to something more
> > accurate, such as gmem_memory_attribute?
>
> I asked Sean about this after getting some fixes off list. Sean said
> gmem_in_place_conversion is named for a host admin to use, and something
> like gmem_memory_attributes is too much implementation details for the
> admin.
>
> Sean, would you reconsider since Yan also asked? If the admin compiled
> the kernel knowing what CONFIG_KVM_VM_MEMORY_ATTRIBUTES means, then the
> admin would also be able to use a param like gmem_memory_attributes?
No, because it's not all memory attributes, it's very specifically the PRIVATE
attribute that will get moved to guest_memfd. I don't want to pick a name that
will become stale and confusing when RWX attributes come along. The RWX bits
will be per-VM, while PRIVATE will be per-guest_memfd.
^ permalink raw reply
* Re: [PATCH v8 18/46] KVM: guest_memfd: Handle lru_add fbatch refcounts during conversion safety check
From: Sean Christopherson @ 2026-06-25 0:35 UTC (permalink / raw)
To: Ackerley Tng
Cc: aik, andrew.jones, binbin.wu, brauner, chao.p.peng, david,
jmattson, jthoughton, michael.roth, oupton, pankaj.gupta, qperret,
rick.p.edgecombe, rientjes, shivankg, steven.price, tabba, willy,
wyihan, yan.y.zhao, forkloop, pratyush, suzuki.poulose,
aneesh.kumar, liam, Paolo Bonzini, Thomas Gleixner, Ingo Molnar,
Borislav Petkov, Dave Hansen, x86, H. Peter Anvin, Steven Rostedt,
Masami Hiramatsu, Mathieu Desnoyers, Jonathan Corbet, Shuah Khan,
Shuah Khan, Vishal Annapurve, Andrew Morton, Chris Li,
Kairui Song, Kemeng Shi, Nhat Pham, Barry Song, Axel Rasmussen,
Yuanchu Xie, Wei Xu, Youngjun Park, Qi Zheng, Shakeel Butt,
Kiryl Shutsemau, Baoquan He, Jason Gunthorpe, Vlastimil Babka,
kvm, linux-kernel, linux-trace-kernel, linux-doc, linux-kselftest,
linux-mm, linux-coco
In-Reply-To: <CAEvNRgE8HZDOnexMJeim6TjmxGG1AUXFY2+HH1YyKB=aM6D-DQ@mail.gmail.com>
On Wed, Jun 24, 2026, Ackerley Tng wrote:
> Sean Christopherson <seanjc@google.com> writes:
>
> > On Thu, Jun 18, 2026, Ackerley Tng wrote:
> >> When checking if a guest_memfd folio is safe for conversion, its refcount
> >> is examined. A folio may be present in a per-CPU lru_add fbatch, which
> >> temporarily increases its refcount.
> >
> > Under what circumstances does this happen,
>
> It happened 100% of the time in selftests. Perhaps it's because in the
> selftests the pages are almost always freshly allocated and so the
> lru_add fbatch isn't full yet? (and that the host isn't super busy so
> lru_add fbatch doesn't get drained yet).
I chatted with Ackerley about this. What I wanted to understand is why guest_memfd
pages were getting put onto per-CPU batches for lru_add(), given that guest_memfd
pages are unevictable. The answer (assuming I read the code right), is that
lruvec_add_folio() updates stats and other per-lru metadata for the unevictable
lru, and does so under a per-lru lock. I.e. we don't want to skip that stuff
entirely.
One thought I had, to avoid the IPIs that draining all per-CPU caches requires,
was to disallow putting guest_memfd pages in folio batches, e.g. by hacking
something into folio_may_be_lru_cached(). But due to taking a per-lru lock,
that would penalize the relatively hot path and definitely common operation of
faulting in guest memory. On the other hand, memory conversion is already a
relatively slow operation and is relatively uncommon compared to page faults,
(and likely very uncommon for real world setups). I.e. having to drain all
caches if conversion isn't safe penalizes a relatively slow, relatively uncommon
path.
If we're concerned about noisy neighbor problems, or outright abuse, I think a
simple (per process?) ratelimit would suffice. But it's not clear to me that we
even need that, because there are already many flows in the kernel that allow
blasting IPIs without too much effort.
^ permalink raw reply
* Re: [PATCH v8 00/46] guest_memfd: In-place conversion support
From: Ackerley Tng @ 2026-06-25 0:19 UTC (permalink / raw)
To: Xiaoyao Li, aik, andrew.jones, binbin.wu, brauner, chao.p.peng,
david, jmattson, jthoughton, michael.roth, oupton, pankaj.gupta,
qperret, rick.p.edgecombe, rientjes, shivankg, steven.price,
tabba, willy, wyihan, yan.y.zhao, forkloop, pratyush,
suzuki.poulose, aneesh.kumar, liam, Paolo Bonzini,
Sean Christopherson, Thomas Gleixner, Ingo Molnar,
Borislav Petkov, Dave Hansen, x86, H. Peter Anvin, Steven Rostedt,
Masami Hiramatsu, Mathieu Desnoyers, Jonathan Corbet, Shuah Khan,
Shuah Khan, Vishal Annapurve, Andrew Morton, Chris Li,
Kairui Song, Kemeng Shi, Nhat Pham, Barry Song, Axel Rasmussen,
Yuanchu Xie, Wei Xu, Youngjun Park, Qi Zheng, Shakeel Butt,
Kiryl Shutsemau, Baoquan He, Jason Gunthorpe, Vlastimil Babka
Cc: kvm, linux-kernel, linux-trace-kernel, linux-doc, linux-kselftest,
linux-mm, linux-coco
In-Reply-To: <9f81ea12-98c4-4ce6-a95e-233851dfe8dd@intel.com>
Xiaoyao Li <xiaoyao.li@intel.com> writes:
> On 6/19/2026 8:31 AM, Ackerley Tng via B4 Relay wrote:
>> TODOs
>>
>> + Retest with TDX selftests. v7 was tested with TDX [12], but the setup there was
>> wrong. Conversions were successful (no errors), but the shared memory being
>> tested is actually in a completely different host physical page.
>
> Glad to see you knew it already (I was going to report this to the
> original POC TDX patch)
Thanks for reviewing!
^ permalink raw reply
* Re: [PATCH v8 00/46] guest_memfd: In-place conversion support
From: Ackerley Tng @ 2026-06-25 0:19 UTC (permalink / raw)
To: Garg, Shivank, aik, andrew.jones, binbin.wu, brauner, chao.p.peng,
david, jmattson, jthoughton, michael.roth, oupton, pankaj.gupta,
qperret, rick.p.edgecombe, rientjes, steven.price, tabba, willy,
wyihan, yan.y.zhao, forkloop, pratyush, suzuki.poulose,
aneesh.kumar, liam, Paolo Bonzini, Sean Christopherson,
Thomas Gleixner, Ingo Molnar, Borislav Petkov, Dave Hansen, x86,
H. Peter Anvin, Steven Rostedt, Masami Hiramatsu,
Mathieu Desnoyers, Jonathan Corbet, Shuah Khan, Shuah Khan,
Vishal Annapurve, Andrew Morton, Chris Li, Kairui Song,
Kemeng Shi, Nhat Pham, Barry Song, Axel Rasmussen, Yuanchu Xie,
Wei Xu, Youngjun Park, Qi Zheng, Shakeel Butt, Kiryl Shutsemau,
Baoquan He, Jason Gunthorpe, Vlastimil Babka
Cc: kvm, linux-kernel, linux-trace-kernel, linux-doc, linux-kselftest,
linux-mm, linux-coco
In-Reply-To: <a6373206-60b6-454c-9aa9-9d52f9d84de3@amd.com>
"Garg, Shivank" <shivankg@amd.com> writes:
>
> [...snip...]
>
>
> Hi,
>
> Thanks for this series.
>
> [...snip...]
>
>
> Tested-by: Shivank Garg <shivankg@amd.com>
Thanks for testing!
>
> Best regards,
> Shivank
^ permalink raw reply
* Re: [PATCH v8 24/46] KVM: guest_memfd: Make in-place conversion the default
From: Ackerley Tng @ 2026-06-25 0:05 UTC (permalink / raw)
To: Yan Zhao
Cc: aik, andrew.jones, binbin.wu, brauner, chao.p.peng, david,
jmattson, jthoughton, michael.roth, oupton, pankaj.gupta, qperret,
rick.p.edgecombe, rientjes, shivankg, steven.price, tabba, willy,
wyihan, forkloop, pratyush, suzuki.poulose, aneesh.kumar, liam,
Paolo Bonzini, Sean Christopherson, Thomas Gleixner, Ingo Molnar,
Borislav Petkov, Dave Hansen, x86, H. Peter Anvin, Steven Rostedt,
Masami Hiramatsu, Mathieu Desnoyers, Jonathan Corbet, Shuah Khan,
Shuah Khan, Vishal Annapurve, Andrew Morton, Chris Li,
Kairui Song, Kemeng Shi, Nhat Pham, Barry Song, Axel Rasmussen,
Yuanchu Xie, Wei Xu, Youngjun Park, Qi Zheng, Shakeel Butt,
Kiryl Shutsemau, Baoquan He, Jason Gunthorpe, Vlastimil Babka,
kvm, linux-kernel, linux-trace-kernel, linux-doc, linux-kselftest,
linux-mm, linux-coco
In-Reply-To: <aji/2svhcc84rn5w@yzhao56-desk.sh.intel.com>
Yan Zhao <yan.y.zhao@intel.com> writes:
>
> [...snip...]
>
>>
>> #ifdef kvm_arch_has_private_mem
>> -bool __ro_after_init gmem_in_place_conversion = false;
>> +bool __ro_after_init gmem_in_place_conversion = !IS_ENABLED(CONFIG_KVM_VM_MEMORY_ATTRIBUTES);
>> +module_param(gmem_in_place_conversion, bool, 0444);
>
> With gmem_in_place_conversion=true, userspace can create guest_memfd without the
> MMAP flag. In such cases, shared memory is allocated from different backends.
> This means this module parameter only enables per-gmem memory attribute and does
> not guarantee that gmem in-place conversion will actually occur.
>
> To avoid confusion, could we rename this module parameter to something more
> accurate, such as gmem_memory_attribute?
>
I asked Sean about this after getting some fixes off list. Sean said
gmem_in_place_conversion is named for a host admin to use, and something
like gmem_memory_attributes is too much implementation details for the
admin.
Sean, would you reconsider since Yan also asked? If the admin compiled
the kernel knowing what CONFIG_KVM_VM_MEMORY_ATTRIBUTES means, then the
admin would also be able to use a param like gmem_memory_attributes?
There's the additional benefit that the similar naming aids in
understanding for both the admin and software engineers.
Either way, in the next revision, I'll also add this documentation for
this module_param:
Setting the module parameter gmem_in_place_conversion to true will
enable the KVM_SET_MEMORY_ATTRIBUTES2 guest_memfd ioctl and disables
the KVM_SET_MEMORY_ATTRIBUTES VM ioctl. If gmem_in_place_conversion is
true, the private/shared attribute will be tracked per-guest_memfd
instead of per-VM.
Let me know what y'all think of the wording!
>>
>> [...snip...]
>>
^ permalink raw reply
* Re: [PATCH v8 01/10] tracing/probes: Make the $ prefix mandatory for comm access
From: Masami Hiramatsu @ 2026-06-24 23:33 UTC (permalink / raw)
To: Masami Hiramatsu (Google)
Cc: Steven Rostedt, Mathieu Desnoyers, Jonathan Corbet, Shuah Khan,
linux-kernel, linux-trace-kernel, linux-doc, linux-kselftest
In-Reply-To: <178231209724.732967.12049805699091810641.stgit@devnote2>
On Wed, 24 Jun 2026 23:41:37 +0900
"Masami Hiramatsu (Google)" <mhiramat@kernel.org> wrote:
> From: Masami Hiramatsu (Google) <mhiramat@kernel.org>
>
> Since $comm or $COMM are not event field but special fetcharg
> variables to access current->comm, It should not be accessed
> without '$' prefix even with typecast.
>
Let me pick this to probes/core.
Thanks,
> Fixes: 69efd863a785 ("tracing/eprobes: Allow use of BTF names to dereference pointers")
> Signed-off-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
> ---
> Changes in v8:
> - Newly added.
> ---
> kernel/trace/trace_probe.c | 12 +++++++-----
> 1 file changed, 7 insertions(+), 5 deletions(-)
>
> diff --git a/kernel/trace/trace_probe.c b/kernel/trace/trace_probe.c
> index c10bbb0df7b9..0da7c0b53ba7 100644
> --- a/kernel/trace/trace_probe.c
> +++ b/kernel/trace/trace_probe.c
> @@ -342,10 +342,6 @@ static int parse_trace_event(char *arg, struct fetch_insn *code,
> ret = parse_trace_event_arg(arg, code, ctx);
> if (!ret)
> return 0;
> - if (strcmp(arg, "comm") == 0 || strcmp(arg, "COMM") == 0) {
> - code->op = FETCH_OP_COMM;
> - return 0;
> - }
> return -EINVAL;
> }
>
> @@ -1065,8 +1061,14 @@ static int parse_probe_vars(char *orig_arg, const struct fetch_type *t,
> int len;
>
> if (ctx->flags & TPARG_FL_TEVENT) {
> - if (parse_trace_event(arg, code, ctx) < 0)
> + if (parse_trace_event(arg, code, ctx) < 0) {
> + /* 'comm' should be checked after field parsing. */
> + if (strcmp(arg, "comm") == 0 || strcmp(arg, "COMM") == 0) {
> + code->op = FETCH_OP_COMM;
> + return 0;
> + }
> goto inval;
> + }
> return 0;
> }
>
>
--
Masami Hiramatsu (Google) <mhiramat@kernel.org>
^ permalink raw reply
* Re: [PATCH v8 23/46] KVM: TDX: Make source page optional for KVM_TDX_INIT_MEM_REGION
From: Ackerley Tng @ 2026-06-24 23:00 UTC (permalink / raw)
To: Sean Christopherson, Yan Zhao
Cc: aik, andrew.jones, binbin.wu, brauner, chao.p.peng, david,
jmattson, jthoughton, michael.roth, oupton, pankaj.gupta, qperret,
rick.p.edgecombe, rientjes, shivankg, steven.price, tabba, willy,
wyihan, forkloop, pratyush, suzuki.poulose, aneesh.kumar, liam,
Paolo Bonzini, Thomas Gleixner, Ingo Molnar, Borislav Petkov,
Dave Hansen, x86, H. Peter Anvin, Steven Rostedt,
Masami Hiramatsu, Mathieu Desnoyers, Jonathan Corbet, Shuah Khan,
Shuah Khan, Vishal Annapurve, Andrew Morton, Chris Li,
Kairui Song, Kemeng Shi, Nhat Pham, Barry Song, Axel Rasmussen,
Yuanchu Xie, Wei Xu, Youngjun Park, Qi Zheng, Shakeel Butt,
Kiryl Shutsemau, Baoquan He, Jason Gunthorpe, Vlastimil Babka,
kvm, linux-kernel, linux-trace-kernel, linux-doc, linux-kselftest,
linux-mm, linux-coco
In-Reply-To: <ajxasFBzp_9KnQLq@google.com>
Sean Christopherson <seanjc@google.com> writes:
> On Tue, Jun 23, 2026, Yan Zhao wrote:
>> On Tue, Jun 23, 2026 at 01:16:14PM +0800, Yan Zhao wrote:
>> > On Mon, Jun 22, 2026 at 06:22:45PM -0700, Sean Christopherson wrote:
>> > > On Mon, Jun 22, 2026, Yan Zhao wrote:
>> > > > On Thu, Jun 18, 2026 at 05:32:00PM -0700, Ackerley Tng via B4 Relay wrote:
>> > > > > diff --git a/arch/x86/kvm/vmx/tdx.c b/arch/x86/kvm/vmx/tdx.c
>> > > > > index ffe9d0db58c59..56d10333c61a7 100644
>> > > > > --- a/arch/x86/kvm/vmx/tdx.c
>> > > > > +++ b/arch/x86/kvm/vmx/tdx.c
>> > > > > @@ -3198,8 +3198,12 @@ static int tdx_gmem_post_populate(struct kvm *kvm, gfn_t gfn, kvm_pfn_t pfn,
>> > > > > if (KVM_BUG_ON(kvm_tdx->page_add_src, kvm))
>> > > > > return -EIO;
>> > > > >
>> > > > > - if (!src_page)
>> > > > > - return -EOPNOTSUPP;
>> > > > > + if (!src_page) {
>> > > > > + if (!gmem_in_place_conversion)
>> > > > When userspace turns on gmem_in_place_conversion while creating guest_memfd
>> > > > without the MMAP flag, the absence of src_page should still be treated as an
>> > > > error.
>> > >
>> > > Why MMAP?
>> > Hmm, I was showing a scenario that in-place conversion couldn't occur.
>> > I didn't mean that with the MMAP flag, mmap() and user write must occur.
>> >
>> > > Shouldn't this be a general "if (!src_page && !up-to-date)"? Just
>> > > because userspace _can_ mmap() the memory doesn't mean userspace _has_ mmap()'d
>> > > and written memory. And when write() lands, MMAP wouldn't be necessary to
>> > > initialize the memory.
>> > Do you mean using up-to-date flag as below?
>
> Yes? I didn't actually look at the implementation details.
>
>> > if (!src_page) {
>> > src_page = pfn_to_page(pfn);
>> > if (!folio_test_uptodate(page_folio(src_page)))
>> > return -EOPNOTSUPP;
>> > }
Yan is right that with the earlier patch "Zero page while getting pfn",
folio_test_uptodate() here will always return true.
Actually, this is an alternative fix for the issue Sashiko pointed out
on v7 where userspace can do a populate() (either TDX or SNP) without
first allocating the page, with src_address == NULL, and leak
uninitialized memory into the guest.
Advantage of using the uptodate check in populate: if the host never
allocates the page, populate doesn't incur zeroing before writing the
page anyway in populate().
Disadvantage: Both TDX and SNP will have to implement this uptodate
check. guest_memfd can't check centrally because for SNP, for a
PAGE_TYPE_ZERO, !src_page should be allowed with a !uptodate page since
firmware will zero and there's no leakage of uninitialized host memory?
>>
>> Another concern with this fix is that:
>> commit "KVM: guest_memfd: Zero page while getting pfn" [1] always marks the
>> folio uptodate before reaching post_populate().
>>
>> [1] https://lore.kernel.org/all/20260618-gmem-inplace-conversion-v8-21-9d2959357853@google.com/
>>
>> > One concern is that TDX now does not much care about the up-to-date flag since
>> > TDX doesn't rely on the flag to clear pages on conversions.
>> > I'm not sure if the flag can be reliably checked in this case. e.g.,
>> > now the whole folio is marked up-to-date even if only part of it is faulted by
>> > user access.
>> > Ensuring that the up-to-date flag works correctly with huge page support seems
>> > to have more effort than introducing a dedicated flag for TDX.
>> >
>> > > > Additionally, to properly enable in-place copying for the TDX initial memory
>> > > > region, userspace must not only specify source_addr to NULL, but also follow
>> > > > a specific sequence (where steps 1/2/3/7 are required only for in-place copy):
>> > > > 1. create guest_memfd with MMAP flag
>> > > > 2. mmap the guest_memfd.
>> > > > 3. convert the initial memory range to shared.
>> > > > 4. copy initial content to the source page.
>> > > > 5. convert the initial memory range to private
>> > > > 6. invoke ioctl KVM_TDX_INIT_MEM_REGION.
>> > > > 7. do not unmap the source backend.
>> > > >
>> > > > So, would it be reasonable to introduce a dedicated flag that allows userspace
>> > > > to explicitly opt into the in-place copy functionality? e.g.,
>> > >
>> > > Why? It's userspace's responsibility to get the above right. If userspace fails
>> > > to provide a src_page when it doesn't want in-place copy, that's a userspace bug.
Yan, is your concern that userspace forgot to update the code and
forgets to provide a src_page, and if we keep the "Zero page while
getting pfn" patch, ends up with the guest silently having a zero page?
I think that would be found quite early in userspace VMM testing...
>> > I mean if userspace specifies a NULL source_addr by mistake, it's better for
>> > kernel to detect this mistake, similar to how it validates whether source_addr
>> > is PAGE_ALIGNED.
>
> The alignment case is different. If userspace provides an unaligned value, KVM
> *can't* do what userspace is asking because hardware and thus KVM only supports
> converting on page boundaries.
>
> For a NULL source, KVM can still do what userspace is asking. Rejecting userspace's
> request would then be making assumptions about what userspace wants.
>
Also, +1 on this, what if userspace, knowing that pages are zeroed on
allocation, actually wants to rely on that to get a zero page in the guest?
>> > Since userspace already needs to perform additional steps to enable in-place
>> > copy, specifying a dedicated flag to indicate that the NULL source_addr is
>> > intentional seems like a reasonable burden.
>
> I don't see how it adds any value. I wouldn't be at all surprised if most VMMs
> just wen up with code that does:
>
> if (in-place) {
> src = NULL;
> flags |= KVM_TDX_IN_PLACE_COPY_INITIAL_MEMORY_REGION;
> }
^ permalink raw reply
* Re: [PATCH 7/7] i2c: nomadik: add support for I2C_XFER_V2 - detailed fault reporting
From: Linus Walleij @ 2026-06-24 22:56 UTC (permalink / raw)
To: Dmitry Guzman
Cc: Andi Shyti, Steven Rostedt, Masami Hiramatsu, Mathieu Desnoyers,
linux-i2c, linux-kernel, linux-trace-kernel, linux-arm-kernel
In-Reply-To: <20260623-i2c-fault-reporting-v1-7-6db1a8aabf18@mobileye.com>
On Tue, Jun 23, 2026 at 6:32 PM Dmitry Guzman
<Dmitry.Guzman@mobileye.com> wrote:
> I2C_XFER_V2 is a new API that allows I2C clients to get the detailed
> report in case of transmission failure. Previously, the only information
> returned by I2C bus controller was the error code; there was no way to
> find out how many messages or bytes in a certain message have been sent
> or received until the fault condition occurred.
>
> This commit introduces support of this feature in i2c-nomadik driver.
>
> Signed-off-by: Dmitry Guzman <Dmitry.Guzman@mobileye.com>
I don't fully understand patch 1 but if that is fine, this is fine:
Acked-by: Linus Walleij <linusw@kernel.org>
Yours,
Linus Walleij
^ permalink raw reply
* Re: [PATCH 6/7] i2c: nomadik: add quirks max_len=2047 and no_zero_len_read
From: Linus Walleij @ 2026-06-24 22:55 UTC (permalink / raw)
To: Dmitry Guzman
Cc: Andi Shyti, Steven Rostedt, Masami Hiramatsu, Mathieu Desnoyers,
linux-i2c, linux-kernel, linux-trace-kernel, linux-arm-kernel
In-Reply-To: <20260623-i2c-fault-reporting-v1-6-6db1a8aabf18@mobileye.com>
On Tue, Jun 23, 2026 at 6:32 PM Dmitry Guzman
<Dmitry.Guzman@mobileye.com> wrote:
> In Nomadik I2c controller, register I2C_MCR has 11-bit wide LENGTH
> field. Its maximum value is 2047, so this is the maximum length of a
> single message. It is less than the common maximum I2C message length in
> I2C subsystem (8192), so define a quirk in order to report the
> unsupported message without any attempt to transfer it.
>
> Zero length reading doesn't work properly on this controller, so add
> `I2C_AQ_NO_ZERO_LEN_READ` quirk flag.
>
> Signed-off-by: Dmitry Guzman <Dmitry.Guzman@mobileye.com>
Excellent improvements, almost a Fixes: patch.
Reviewed-by: Linus Walleij <linusw@kernel.org>
Yours,
Linus Walleij
^ permalink raw reply
* Re: [PATCH 5/7] i2c: nomadik: change print level for fault messages to debug
From: Linus Walleij @ 2026-06-24 22:54 UTC (permalink / raw)
To: Dmitry Guzman
Cc: Andi Shyti, Steven Rostedt, Masami Hiramatsu, Mathieu Desnoyers,
linux-i2c, linux-kernel, linux-trace-kernel, linux-arm-kernel
In-Reply-To: <20260623-i2c-fault-reporting-v1-5-6db1a8aabf18@mobileye.com>
On Tue, Jun 23, 2026 at 6:32 PM Dmitry Guzman
<Dmitry.Guzman@mobileye.com> wrote:
> i2c-nomadik driver prints error message on every faulted message. This
> is not a good practice, because in I2C a fault not always is an error,
> sometimes it is the expected result. For example, scanning bus with
> `i2cdetects` prints over 100 messages in dmesg (two messages per each
> target address).
>
> To avoid excessive prints in the log, change the print level from err to
> debug.
>
> Signed-off-by: Dmitry Guzman <Dmitry.Guzman@mobileye.com>
Reviewed-by: Linus Walleij <linusw@kernel.org>
Yours,
Linus Walleij
^ permalink raw reply
* Re: [PATCH 4/7] i2c: nomadik: return proper fault codes
From: Linus Walleij @ 2026-06-24 22:53 UTC (permalink / raw)
To: Dmitry Guzman
Cc: Andi Shyti, Steven Rostedt, Masami Hiramatsu, Mathieu Desnoyers,
linux-i2c, linux-kernel, linux-trace-kernel, linux-arm-kernel
In-Reply-To: <20260623-i2c-fault-reporting-v1-4-6db1a8aabf18@mobileye.com>
On Tue, Jun 23, 2026 at 6:32 PM Dmitry Guzman
<Dmitry.Guzman@mobileye.com> wrote:
> I2C documentation Documentation/i2c/fault-codes.rst defines fault codes
> for different negative results in I2C transmittion. Previously,
> i2c-nomadik driver didn't implement them properly - it returned
> ETIMEDOUT on most errors and EIO on master arbitration lost.
>
> To comply with the documentation, return the proper fault codes for
> different conditions, namely:
>
> - EAGAIN if arbitration lost
> - EOVERFLOW if message is too long (>2047 bytes)
> - ENXIO if target address is not acknowledged
> - EIO on other errors detected by controller (for example, NACK on data)
> - ETIMEDOUT if driver gets timeout waiting for message completion
> without any fault condition detected by the controller (for example,
> too long message, or SDA/SCL line stuck on 0).
>
> Signed-off-by: Dmitry Guzman <Dmitry.Guzman@mobileye.com>
Reviewed-by: Linus Walleij <linusw@kernel.org>
Yours,
Linus Walleij
^ permalink raw reply
* Re: [PATCH 3/7] i2c: nomadik: do not try to retransmit I2C message series on errors
From: Linus Walleij @ 2026-06-24 22:51 UTC (permalink / raw)
To: Dmitry Guzman
Cc: Andi Shyti, Steven Rostedt, Masami Hiramatsu, Mathieu Desnoyers,
linux-i2c, linux-kernel, linux-trace-kernel, linux-arm-kernel
In-Reply-To: <20260623-i2c-fault-reporting-v1-3-6db1a8aabf18@mobileye.com>
On Tue, Jun 23, 2026 at 6:32 PM Dmitry Guzman
<Dmitry.Guzman@mobileye.com> wrote:
> i2c-nomadik driver of I2C bus controller in `xfer` callback retransmits
> the whole message series in cause of any fault, and returns fault only
> after third failed attempt. This behavior contradicts with API because
> not only it hides hardware faults, but also re-sends messages, while
> they are not guaranteed to be idempotent.
>
> Remove the triple attempt to send messages in `xfer` callback.
>
> Signed-off-by: Dmitry Guzman <Dmitry.Guzman@mobileye.com>
This originally came from:
commit ebd10e0783d9fb92a147e60902e22c2d3f3ad69d
Author: Virupax Sadashivpetimath <virupax.sadashivpetimath@stericsson.com>
Date: Fri May 13 12:30:23 2011 +0200
i2c-nomadik: add code to retry on timeout failure
It is seen that i2c-nomadik controller randomly stops generating the
interrupts leading to a i2c timeout. As a workaround to this problem,
add retries to the on going transfer on failure.
Signed-off-by: Virupax Sadashivpetimath
<virupax.sadashivpetimath@stericsson.com>
Reviewed-by: Jonas ABERG <jonas.aberg@stericsson.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Ben Dooks <ben-linux@fluff.org>
At that time the code looked very different:
for (j = 0; j < 3; j++) {
if (status || (dev->result)) {
(...)
break;
}
udelay(I2C_DELAY);
}
if (status == 0)
break;
We would only spin here if both status and dev->result
(the number of sent bytes) was 0. This doesn't seem to be
at all the case anymore!
I suppose it's a bit dubious code, so:
Reviewed-by: Linus Walleij <linusw@kernel.org>
Yours,
Linus Walleij
^ permalink raw reply
* Re: [PATCH 2/7] i2c: nomadik: optimize layout of struct nmk_i2c_dev
From: Linus Walleij @ 2026-06-24 22:36 UTC (permalink / raw)
To: Dmitry Guzman
Cc: Andi Shyti, Steven Rostedt, Masami Hiramatsu, Mathieu Desnoyers,
linux-i2c, linux-kernel, linux-trace-kernel, linux-arm-kernel
In-Reply-To: <20260623-i2c-fault-reporting-v1-2-6db1a8aabf18@mobileye.com>
Hi Dmitry,
thanks for your patch!
Also nice to see some kernel contributions directly from
MobilEye!
On Tue, Jun 23, 2026 at 6:32 PM Dmitry Guzman
<Dmitry.Guzman@mobileye.com> wrote:
> Put two bool variables `xfer_done` and `has_32b_bus` and two char
> variables `tft` and `rft` together in order to reduce struct size
> wasted for padding.
>
> Signed-off-by: Dmitry Guzman <Dmitry.Guzman@mobileye.com>
(...)
> struct nmk_i2c_dev {
> struct i2c_vendor_data *vendor;
> @@ -206,13 +206,13 @@ struct nmk_i2c_dev {
> u32 clk_freq;
> unsigned char tft;
> unsigned char rft;
^
Maybe you want to take the opportunity to change these
two into u8 if you're anyway changing the layout of this
struct?
Either way:
Reviewed-by: Linus Walleij <linusw@kernel.org>
Yours,
Linus Walleij
^ permalink raw reply
* Re: [PATCH v8 22/46] KVM: SEV: Make 'uaddr' parameter optional for KVM_SEV_SNP_LAUNCH_UPDATE
From: Ackerley Tng @ 2026-06-24 22:31 UTC (permalink / raw)
To: Fuad Tabba
Cc: aik, andrew.jones, binbin.wu, brauner, chao.p.peng, david,
jmattson, jthoughton, michael.roth, oupton, pankaj.gupta, qperret,
rick.p.edgecombe, rientjes, shivankg, steven.price, willy, wyihan,
yan.y.zhao, forkloop, pratyush, suzuki.poulose, aneesh.kumar,
liam, Paolo Bonzini, Sean Christopherson, Thomas Gleixner,
Ingo Molnar, Borislav Petkov, Dave Hansen, x86, H. Peter Anvin,
Steven Rostedt, Masami Hiramatsu, Mathieu Desnoyers,
Jonathan Corbet, Shuah Khan, Shuah Khan, Vishal Annapurve,
Andrew Morton, Chris Li, Kairui Song, Kemeng Shi, Nhat Pham,
Barry Song, Axel Rasmussen, Yuanchu Xie, Wei Xu, Youngjun Park,
Qi Zheng, Shakeel Butt, Kiryl Shutsemau, Baoquan He,
Jason Gunthorpe, Vlastimil Babka, kvm, linux-kernel,
linux-trace-kernel, linux-doc, linux-kselftest, linux-mm,
linux-coco
In-Reply-To: <CA+EHjTz3SW50EzxgXm8VysoaM21RReUVG2px_WUYU7zUwjXnpQ@mail.gmail.com>
Fuad Tabba <tabba@google.com> writes:
>
> [...snip...]
>
>> diff --git a/Documentation/virt/kvm/x86/amd-memory-encryption.rst b/Documentation/virt/kvm/x86/amd-memory-encryption.rst
>> index bd04a908a8dbd..29409297f1ef0 100644
>> --- a/Documentation/virt/kvm/x86/amd-memory-encryption.rst
>> +++ b/Documentation/virt/kvm/x86/amd-memory-encryption.rst
>> @@ -503,7 +503,8 @@ secrets.
>>
>> It is required that the GPA ranges initialized by this command have had the
>> KVM_MEMORY_ATTRIBUTE_PRIVATE attribute set in advance. See the documentation
>> -for KVM_SET_MEMORY_ATTRIBUTES for more details on this aspect.
>> +for KVM_SET_MEMORY_ATTRIBUTES/KVM_SET_MEMORY_ATTRIBUTES2 for more details on
>> +this aspect.
>>
>> Upon success, this command is not guaranteed to have processed the entire
>> range requested. Instead, the ``gfn_start``, ``uaddr``, and ``len`` fields of
>> @@ -511,9 +512,13 @@ range requested. Instead, the ``gfn_start``, ``uaddr``, and ``len`` fields of
>> remaining range that has yet to be processed. The caller should continue
>> calling this command until those fields indicate the entire range has been
>> processed, e.g. ``len`` is 0, ``gfn_start`` is equal to the last GFN in the
>> -range plus 1, and ``uaddr`` is the last byte of the userspace-provided source
>> -buffer address plus 1. In the case where ``type`` is KVM_SEV_SNP_PAGE_TYPE_ZERO,
>> -``uaddr`` will be ignored completely.
>> +range plus 1, and ``uaddr`` (if specified) is the last byte of the
>> +userspace-provided source buffer address plus 1.
>> +
>> +In the case where ``type`` is KVM_SEV_SNP_PAGE_TYPE_ZERO, ``uaddr`` will be
>> +ignored completely. For all other page types, ``uaddr`` is optional if in-place
>> +conversion is enable, i.e. when the destination can also be the source, and is
>
> Typo: "is enable" -> "is enabled".
>
> "when the destination can also be the source" is hard to parse without
> context. Maybe: "i.e. when the data has been written directly to
> guest_memfd while the range was in the shared state".
>
> Also, how does userspace discover whether in-place conversion is
> enabled? A cross-reference to KVM_CAP_GUEST_MEMFD_MEMORY_ATTRIBUTES
> would help here.
>
Will fix in the next revision. Thanks!
> Cheers,
> /fuad
>
>>
>> [...snip...]
>>
^ permalink raw reply
* Re: [PATCH v8 23/46] KVM: TDX: Make source page optional for KVM_TDX_INIT_MEM_REGION
From: Sean Christopherson @ 2026-06-24 22:31 UTC (permalink / raw)
To: Yan Zhao
Cc: ackerleytng, aik, andrew.jones, binbin.wu, brauner, chao.p.peng,
david, jmattson, jthoughton, michael.roth, oupton, pankaj.gupta,
qperret, rick.p.edgecombe, rientjes, shivankg, steven.price,
tabba, willy, wyihan, forkloop, pratyush, suzuki.poulose,
aneesh.kumar, liam, Paolo Bonzini, Thomas Gleixner, Ingo Molnar,
Borislav Petkov, Dave Hansen, x86, H. Peter Anvin, Steven Rostedt,
Masami Hiramatsu, Mathieu Desnoyers, Jonathan Corbet, Shuah Khan,
Shuah Khan, Vishal Annapurve, Andrew Morton, Chris Li,
Kairui Song, Kemeng Shi, Nhat Pham, Barry Song, Axel Rasmussen,
Yuanchu Xie, Wei Xu, Youngjun Park, Qi Zheng, Shakeel Butt,
Kiryl Shutsemau, Baoquan He, Jason Gunthorpe, Vlastimil Babka,
kvm, linux-kernel, linux-trace-kernel, linux-doc, linux-kselftest,
linux-mm, linux-coco
In-Reply-To: <ajpGxu2uQys+S2F8@yzhao56-desk.sh.intel.com>
On Tue, Jun 23, 2026, Yan Zhao wrote:
> On Tue, Jun 23, 2026 at 01:16:14PM +0800, Yan Zhao wrote:
> > On Mon, Jun 22, 2026 at 06:22:45PM -0700, Sean Christopherson wrote:
> > > On Mon, Jun 22, 2026, Yan Zhao wrote:
> > > > On Thu, Jun 18, 2026 at 05:32:00PM -0700, Ackerley Tng via B4 Relay wrote:
> > > > > diff --git a/arch/x86/kvm/vmx/tdx.c b/arch/x86/kvm/vmx/tdx.c
> > > > > index ffe9d0db58c59..56d10333c61a7 100644
> > > > > --- a/arch/x86/kvm/vmx/tdx.c
> > > > > +++ b/arch/x86/kvm/vmx/tdx.c
> > > > > @@ -3198,8 +3198,12 @@ static int tdx_gmem_post_populate(struct kvm *kvm, gfn_t gfn, kvm_pfn_t pfn,
> > > > > if (KVM_BUG_ON(kvm_tdx->page_add_src, kvm))
> > > > > return -EIO;
> > > > >
> > > > > - if (!src_page)
> > > > > - return -EOPNOTSUPP;
> > > > > + if (!src_page) {
> > > > > + if (!gmem_in_place_conversion)
> > > > When userspace turns on gmem_in_place_conversion while creating guest_memfd
> > > > without the MMAP flag, the absence of src_page should still be treated as an
> > > > error.
> > >
> > > Why MMAP?
> > Hmm, I was showing a scenario that in-place conversion couldn't occur.
> > I didn't mean that with the MMAP flag, mmap() and user write must occur.
> >
> > > Shouldn't this be a general "if (!src_page && !up-to-date)"? Just
> > > because userspace _can_ mmap() the memory doesn't mean userspace _has_ mmap()'d
> > > and written memory. And when write() lands, MMAP wouldn't be necessary to
> > > initialize the memory.
> > Do you mean using up-to-date flag as below?
Yes? I didn't actually look at the implementation details.
> > if (!src_page) {
> > src_page = pfn_to_page(pfn);
> > if (!folio_test_uptodate(page_folio(src_page)))
> > return -EOPNOTSUPP;
> > }
>
> Another concern with this fix is that:
> commit "KVM: guest_memfd: Zero page while getting pfn" [1] always marks the
> folio uptodate before reaching post_populate().
>
> [1] https://lore.kernel.org/all/20260618-gmem-inplace-conversion-v8-21-9d2959357853@google.com/
>
> > One concern is that TDX now does not much care about the up-to-date flag since
> > TDX doesn't rely on the flag to clear pages on conversions.
> > I'm not sure if the flag can be reliably checked in this case. e.g.,
> > now the whole folio is marked up-to-date even if only part of it is faulted by
> > user access.
> > Ensuring that the up-to-date flag works correctly with huge page support seems
> > to have more effort than introducing a dedicated flag for TDX.
> >
> > > > Additionally, to properly enable in-place copying for the TDX initial memory
> > > > region, userspace must not only specify source_addr to NULL, but also follow
> > > > a specific sequence (where steps 1/2/3/7 are required only for in-place copy):
> > > > 1. create guest_memfd with MMAP flag
> > > > 2. mmap the guest_memfd.
> > > > 3. convert the initial memory range to shared.
> > > > 4. copy initial content to the source page.
> > > > 5. convert the initial memory range to private
> > > > 6. invoke ioctl KVM_TDX_INIT_MEM_REGION.
> > > > 7. do not unmap the source backend.
> > > >
> > > > So, would it be reasonable to introduce a dedicated flag that allows userspace
> > > > to explicitly opt into the in-place copy functionality? e.g.,
> > >
> > > Why? It's userspace's responsibility to get the above right. If userspace fails
> > > to provide a src_page when it doesn't want in-place copy, that's a userspace bug.
> > I mean if userspace specifies a NULL source_addr by mistake, it's better for
> > kernel to detect this mistake, similar to how it validates whether source_addr
> > is PAGE_ALIGNED.
The alignment case is different. If userspace provides an unaligned value, KVM
*can't* do what userspace is asking because hardware and thus KVM only supports
converting on page boundaries.
For a NULL source, KVM can still do what userspace is asking. Rejecting userspace's
request would then be making assumptions about what userspace wants.
> > Since userspace already needs to perform additional steps to enable in-place
> > copy, specifying a dedicated flag to indicate that the NULL source_addr is
> > intentional seems like a reasonable burden.
I don't see how it adds any value. I wouldn't be at all surprised if most VMMs
just wen up with code that does:
if (in-place) {
src = NULL;
flags |= KVM_TDX_IN_PLACE_COPY_INITIAL_MEMORY_REGION;
}
^ permalink raw reply
* Re: [PATCH v8 21/46] KVM: guest_memfd: Zero page while getting pfn
From: Ackerley Tng @ 2026-06-24 22:30 UTC (permalink / raw)
To: Yan Zhao
Cc: aik, andrew.jones, binbin.wu, brauner, chao.p.peng, david,
jmattson, jthoughton, michael.roth, oupton, pankaj.gupta, qperret,
rick.p.edgecombe, rientjes, shivankg, steven.price, tabba, willy,
wyihan, forkloop, pratyush, suzuki.poulose, aneesh.kumar, liam,
Paolo Bonzini, Sean Christopherson, Thomas Gleixner, Ingo Molnar,
Borislav Petkov, Dave Hansen, x86, H. Peter Anvin, Steven Rostedt,
Masami Hiramatsu, Mathieu Desnoyers, Jonathan Corbet, Shuah Khan,
Shuah Khan, Vishal Annapurve, Andrew Morton, Chris Li,
Kairui Song, Kemeng Shi, Nhat Pham, Barry Song, Axel Rasmussen,
Yuanchu Xie, Wei Xu, Youngjun Park, Qi Zheng, Shakeel Butt,
Kiryl Shutsemau, Baoquan He, Jason Gunthorpe, Vlastimil Babka,
kvm, linux-kernel, linux-trace-kernel, linux-doc, linux-kselftest,
linux-mm, linux-coco
In-Reply-To: <ajpKK/SyRh8LExrY@yzhao56-desk.sh.intel.com>
Yan Zhao <yan.y.zhao@intel.com> writes:
> On Thu, Jun 18, 2026 at 05:31:58PM -0700, Ackerley Tng via B4 Relay wrote:
>> From: Ackerley Tng <ackerleytng@google.com>
>>
>> Move the folio initialization logic from kvm_gmem_get_pfn() into
>> __kvm_gmem_get_pfn() to also zero pages if the page is to be used in
>> kvm_gmem_populate().
>>
>> With in-place conversion, the existing data in a guest_memfd page can be
>> populated into guest memory through platform-specific ioctls.
>>
>> Without first zeroing the page obtained using __kvm_gmem_get_pfn(), it
>> might contain uninitialized host memory, which would leak to the guest if
>> the populate completes.
>>
>> guest_memfd pages are zeroed at most once in the page's entire lifetime
>> with guest_memfd, and that is tracked using the uptodate flag.
>>
>> Zeroing the page in __kvm_gmem_get_pfn() is chosen over zeroing in
>> kvm_gmem_get_folio() since other flows, such as a future write() syscall,
>> can get a page, write to the page and then set page uptodate without
>> zeroing.
>>
>> This aligns with the concept of zeroing before first use - the other place
>> where zeroing happens is in kvm_gmem_fault_user_mapping().
>>
>> Signed-off-by: Ackerley Tng <ackerleytng@google.com>
>> ---
>> virt/kvm/guest_memfd.c | 10 +++++-----
>> 1 file changed, 5 insertions(+), 5 deletions(-)
>>
>> diff --git a/virt/kvm/guest_memfd.c b/virt/kvm/guest_memfd.c
>> index 90bc1a26512b6..86c9f5b0863cb 100644
>> --- a/virt/kvm/guest_memfd.c
>> +++ b/virt/kvm/guest_memfd.c
>> @@ -1137,6 +1137,11 @@ static struct folio *__kvm_gmem_get_pfn(struct file *file,
>> return ERR_PTR(-EHWPOISON);
>> }
>>
>> + if (!folio_test_uptodate(folio)) {
>> + clear_highpage(folio_page(folio, 0));
>> + folio_mark_uptodate(folio);
>> + }
> Note:
> In the __kvm_gmem_populate() path, this folio_mark_uptodate() call makes the
> later one after post_populate() pointless.
>
> __kvm_gmem_populate
> |1.__kvm_gmem_get_pfn
> | |->folio = kvm_gmem_get_folio()
> | | if (!folio_test_uptodate(folio))
> | | folio_mark_uptodate(folio);
> |2. ret = post_populate()
> |3. if (!ret)
> | folio_mark_uptodate(folio);
>
Good point! I'll remove the folio_mark_uptodate() in the populate path
then. Thanks!
>>
>> [...snip...]
>>
^ permalink raw reply
* Re: [PATCH v8 18/46] KVM: guest_memfd: Handle lru_add fbatch refcounts during conversion safety check
From: Ackerley Tng @ 2026-06-24 22:25 UTC (permalink / raw)
To: Sean Christopherson
Cc: aik, andrew.jones, binbin.wu, brauner, chao.p.peng, david,
jmattson, jthoughton, michael.roth, oupton, pankaj.gupta, qperret,
rick.p.edgecombe, rientjes, shivankg, steven.price, tabba, willy,
wyihan, yan.y.zhao, forkloop, pratyush, suzuki.poulose,
aneesh.kumar, liam, Paolo Bonzini, Thomas Gleixner, Ingo Molnar,
Borislav Petkov, Dave Hansen, x86, H. Peter Anvin, Steven Rostedt,
Masami Hiramatsu, Mathieu Desnoyers, Jonathan Corbet, Shuah Khan,
Shuah Khan, Vishal Annapurve, Andrew Morton, Chris Li,
Kairui Song, Kemeng Shi, Nhat Pham, Barry Song, Axel Rasmussen,
Yuanchu Xie, Wei Xu, Youngjun Park, Qi Zheng, Shakeel Butt,
Kiryl Shutsemau, Baoquan He, Jason Gunthorpe, Vlastimil Babka,
kvm, linux-kernel, linux-trace-kernel, linux-doc, linux-kselftest,
linux-mm, linux-coco
In-Reply-To: <ajwMYCSrPlxg-Fok@google.com>
Sean Christopherson <seanjc@google.com> writes:
> On Thu, Jun 18, 2026, Ackerley Tng wrote:
>> When checking if a guest_memfd folio is safe for conversion, its refcount
>> is examined. A folio may be present in a per-CPU lru_add fbatch, which
>> temporarily increases its refcount.
>
> Under what circumstances does this happen,
It happened 100% of the time in selftests. Perhaps it's because in the
selftests the pages are almost always freshly allocated and so the
lru_add fbatch isn't full yet? (and that the host isn't super busy so
lru_add fbatch doesn't get drained yet).
I've not tested without this beyond selftests.
I don't think we can depend on workloads to drain the lru_add fbatch?
> and what alternatives are there for
> userspace to work around the issue?
The thing is, the refcounts don't come with a label of who added the
refcount so we can't really return a different error for lru_add fbatch
presence. All folios get added to the lru_add fbatch even if they're
unevictable and eventually not participate in LRU.
We could make userspace try fadvise(POSIX_FADV_DONTNEED)? I think that
has other problems, and this kind of makes userspace have one more user
to guess. Userspace already needs to check if the page is pinned for
DMA, and if it's not pinned for DMA, userspace already needs to retry
because of other possible kernel users...
^ permalink raw reply
* Re: [PATCH v8 15/46] KVM: guest_memfd: Call arch invalidate hooks on conversion
From: Suzuki K Poulose @ 2026-06-24 22:15 UTC (permalink / raw)
To: Ackerley Tng, Sean Christopherson, Fuad Tabba
Cc: aik, andrew.jones, binbin.wu, brauner, chao.p.peng, david,
jmattson, jthoughton, michael.roth, oupton, pankaj.gupta, qperret,
rick.p.edgecombe, rientjes, shivankg, steven.price, willy, wyihan,
yan.y.zhao, forkloop, pratyush, aneesh.kumar, liam, Paolo Bonzini,
Thomas Gleixner, Ingo Molnar, Borislav Petkov, Dave Hansen, x86,
H. Peter Anvin, Steven Rostedt, Masami Hiramatsu,
Mathieu Desnoyers, Jonathan Corbet, Shuah Khan, Shuah Khan,
Vishal Annapurve, Andrew Morton, Chris Li, Kairui Song,
Kemeng Shi, Nhat Pham, Barry Song, Axel Rasmussen, Yuanchu Xie,
Wei Xu, Youngjun Park, Qi Zheng, Shakeel Butt, Kiryl Shutsemau,
Baoquan He, Jason Gunthorpe, Vlastimil Babka, kvm, linux-kernel,
linux-trace-kernel, linux-doc, linux-kselftest, linux-mm,
linux-coco
In-Reply-To: <CAEvNRgGX3GkazCWM=6y9YLgn=YemXuG==Oo+L58cac1Fd86_TQ@mail.gmail.com>
On 24/06/2026 18:46, Ackerley Tng wrote:
> Sean Christopherson <seanjc@google.com> writes:
>
>> On Fri, Jun 19, 2026, Fuad Tabba wrote:
>>> On Fri, 19 Jun 2026 at 01:31, Ackerley Tng via B4 Relay
>>> <devnull+ackerleytng.google.com@kernel.org> wrote:
>>>>
>>>> From: Ackerley Tng <ackerleytng@google.com>
>>>>
>>>> When memory in guest_memfd is converted from private to shared, the
>>>> platform-specific state associated with the guest-private pages must be
>>>> invalidated or cleaned up.
>>>>
>>>> Iterate over the folios in the affected range and call the
>>>> kvm_arch_gmem_invalidate() hook for each PFN range. This allows
>>>> architectures to perform necessary teardown, such as updating hardware
>>>> metadata or encryption states, before the pages are transitioned to the
>>>> shared state.
>>>>
>>>> Invoke this helper after indicating to KVM's mmu code that an invalidation
>>>> is in progress to stop in-flight page faults from succeeding.
>>>>
>>>> Reviewed-by: Fuad Tabba <tabba@google.com>
>>>> Signed-off-by: Ackerley Tng <ackerleytng@google.com>
>>>
>>> Coming back to this after working through the arm64/pKVM side. My
>>> Reviewed-by here is from the previous round and the patch hasn't
>>> changed, but I missed an implication for arm64.
>>>
>>> kvm_arch_gmem_invalidate() is now called from two paths with the same
>>> (start, end) signature: folio teardown (kvm_gmem_free_folio) and
>>> private->shared conversion (here). For SNP/TDX that's fine, conversion is
>>> destructive anyway. For pKVM the two need opposite content semantics:
>>> conversion must preserve the page in place (same physical page, the point
>>> of in-place conversion without encryption), while teardown must scrub it
>>> before returning it to the host.
>>>
>>> The hook gets only a pfn range with no indication of which caller it's
>>> serving, so arm64 can't give the two paths the behaviour they need. It
>>> would help to signal intent on the conversion path: a reason/flag, a
>>> separate hook, or not routing non-destructive conversion through the
>>> teardown hook.
>>>
>>> arm64 isn't here yet, so this isn't urgent, but the hook is gaining a
>>> second caller now, and it's cheaper to leave room for the distinction
>>> than to change a generic contract other arches depend on later.
>>
>> Crud. It may not be urgent for arm64, but it's urgent for other reasons that
>> I "can't" describe in detail at the moment, and even if that weren't the case, I
>> think we should clean things up now. More below.
>>
>>>> virt/kvm/guest_memfd.c | 41 +++++++++++++++++++++++++++++++++++++++++
>>>> 1 file changed, 41 insertions(+)
>>>>
>>>> diff --git a/virt/kvm/guest_memfd.c b/virt/kvm/guest_memfd.c
>>>> index 433f79047b9d1..3c94442bc8131 100644
>>>> --- a/virt/kvm/guest_memfd.c
>>>> +++ b/virt/kvm/guest_memfd.c
>>>> @@ -607,6 +607,42 @@ static bool kvm_gmem_is_safe_for_conversion(struct inode *inode, pgoff_t start,
>>>> return safe;
>>>> }
>>>>
>>>> +#ifdef CONFIG_HAVE_KVM_ARCH_GMEM_INVALIDATE
>>>> +static void kvm_gmem_invalidate(struct inode *inode, pgoff_t start, pgoff_t end)
>>
>> Not your fault, but kvm_arch_gmem_invalidate() is badly misnamed. It's not
>> "invalidating" anything, it's much more of a "free" callback, as SNP uses it to
>> put physical pages back into a shared state when a maybe-private folio is freed.
>>
>> As Fuad points out, (ab)using that hook for the private=>shared conversion case
>> "works", but not broadly. And it makes the bad name worse, because it's called
>> from code that _is_ doing true invalidations. For pKVM, it may not even need to
>> do anything invalidation-like.
>>
>
> Thanks, I also didn't like the naming of kvm_gmem_invalidate(),
> especially when conversions also calls
> kvm_gmem_invalidate_{start,end}() and those do different things.
>
>> To avoid a conflict with patches that are going to have priority over this series,
>> to set the stage for arm64 support, and to avoid avoid bleeding vendor details
>> into guest_memfd, as if they are core guest_memfd behavior (only SNP needs the
>> "invalidation" on this specific transition), I think we should add an arch hook
>> to do conversions straightaway.
>>
>> Unless there's a clever option I'm missing, it'll mean adding yet another
>> HAVE_KVM_ARCH_GMEM_XXX flag? Hmm, especially because IIUC, arm64/pKVM doesn't
>> need a callback for this case, only the free_folio case.
>>
>>>> +{
>>>> + struct folio_batch fbatch;
>>>> + pgoff_t next = start;
>>>> + int i;
>>>> +
>>>> + folio_batch_init(&fbatch);
>>>> + while (filemap_get_folios(inode->i_mapping, &next, end - 1, &fbatch)) {
>>>> + for (i = 0; i < folio_batch_count(&fbatch); ++i) {
>>>> + struct folio *folio = fbatch.folios[i];
>>>> + pgoff_t start_index, end_index;
>>>> + kvm_pfn_t start_pfn, end_pfn;
>>>> +
>>>> + start_index = max(start, folio->index);
>>>> + end_index = min(end, folio_next_index(folio));
>>>> + /*
>>>> + * end_index is either in folio or points to
>>>> + * the first page of the next folio. Hence,
>>>> + * all pages in range [start_index, end_index)
>>>> + * are contiguous.
>>>> + */
>>>> + start_pfn = folio_file_pfn(folio, start_index);
>>>> + end_pfn = start_pfn + end_index - start_index;
>>>> +
>>>> + kvm_arch_gmem_invalidate(start_pfn, end_pfn);
>>>> + }
>>>> +
>>>> + folio_batch_release(&fbatch);
>>>> + cond_resched();
>>>> + }
>>>> +}
>>>> +#else
>>>> +static void kvm_gmem_invalidate(struct inode *inode, pgoff_t start, pgoff_t end) {}
>>>> +#endif
>>>> +
>>>> static int __kvm_gmem_set_attributes(struct inode *inode, pgoff_t start,
>>>> size_t nr_pages, uint64_t attrs,
>>>> pgoff_t *err_index)
>>>> @@ -647,7 +683,12 @@ static int __kvm_gmem_set_attributes(struct inode *inode, pgoff_t start,
>>>> */
>>>>
>>>> kvm_gmem_invalidate_start(inode, start, end);
>>>> +
>>>> + if (!to_private)
>>>> + kvm_gmem_invalidate(inode, start, end);
>>
>> E.g. instead make this something like this?
>>
>> kvm_gmem_set_pfn_attributes(...)
>>
>> Hrm, though that wastes folio lookups in the to_private case. So maybe just this,
>> assuming pKVM doesn't need to take additional action on conversions?
>>
>> if (!to_private)
>> kvm_gmem_make_shared(...)
>>
>> Actually, if we do that, then we don't need a separate arch hook, just a separate
>> config. It'll still bleed SNP details into guest_memfd, but it'll at least be
>> done in a way that's more explicitly arch specific (and it's no different than
>> what we already do for PREPARE...).
>>
>
> pKVM needs some arch guest_memfd lifecycle functions that
>
> + for conversion, doesn't do anything,
> + for teardown, resets page state (IIUC it'll be reset to
> PKVM_PAGE_OWNED (by the host))
>
> So I think we need different functions for those two stages in the
> lifecycle of a page with guest_memfd? What if we have
>
> CONFIG_HAVE_KVM_ARCH_GMEM_SET_PFN_ATTRIBUTES, which gates
>
> + kvm_gmem_should_set_pfn_attributes(attributes) and
> .gmem_should_set_pfn_attributes
> + kvm_gmem_set_pfn_attributes(start_pfn, end_pfn, attributes) and
> .gmem_set_pfn_attributes
>
> CONFIG_HAVE_KVM_ARCH_GMEM_TEARDOWN, which gates
>
> + kvm_gmem_teardown() and .gmem_teardown
>
> SNP:
>
> + .gmem_should_set_pfn_attributes = sev_gmem_should_set_pfn_attributes,
> and sev_gmem_should_set_pfn_attributes returns !is_private
> + Rename .gmem_invalidate and sev_gmem_invalidate to *set_pfn_attributes
> + .gmem_teardown = sev_gmem_set_pfn_attributes
>
> TDX:
>
> + Disable CONFIG_HAVE_KVM_ARCH_GMEM_SET_PFN_ATTRIBUTES
> + Disable CONFIG_HAVE_KVM_ARCH_GMEM_TEARDOWN
>
> pKVM:
>
> + Disable CONFIG_HAVE_KVM_ARCH_GMEM_SET_PFN_ATTRIBUTES
> + .gmem_teardown = pkvm_gmem_set_pfn_attributes
>
> Suzuki, does this work for ARM CCA?
Yep, that works for us. For CCA we would :
+ Disable CONFIG_HAVE_KVM_ARCH_GMEM_SET_PFN_ATTRIBUTES
+ Disable CONFIG_HAVE_KVM_ARCH_GMEM_TEARDOWN
In the future we might utilise the gmem_set_pfn_attributes call back.
Thanks
Suzuki
>
> This way,
>
> + The if (is_private) check doesn't leak SNP details into guest_memfd
> + .gmem_make_shared doesn't stick out without a .gmem_make_private
> + .gmem_set_pfn_attributes, .gmem_prepare and .gmem_teardown are aligned
> conceptually as lifecycle hooks
>
> + I think the private/shared check for prepare can also be folded into
> preparation.
> + Preparation perhaps doesn't need a should_prepare equivalent since
> there's no iteration and getting the gfn is just doing some math?
> + In another patch series?
>
>> E.g. this? There will still be a looming rename conflict, but that's easy enough
>> to handle.
>>
>> diff --git virt/kvm/guest_memfd.c virt/kvm/guest_memfd.c
>> index 9ce5be7843f2..8aead0abd788 100644
>> --- virt/kvm/guest_memfd.c
>> +++ virt/kvm/guest_memfd.c
>> @@ -648,8 +648,8 @@ static bool kvm_gmem_is_safe_for_conversion(struct inode *inode, pgoff_t start,
>> return safe;
>> }
>>
>> -#ifdef CONFIG_HAVE_KVM_ARCH_GMEM_INVALIDATE
>> -static void kvm_gmem_invalidate(struct inode *inode, pgoff_t start, pgoff_t end)
>> +#ifdef CONFIG_KVM_ARCH_GMEM_FREE_ON_SHARED_CONVERSION
>> +static void kvm_gmem_make_shared(struct inode *inode, pgoff_t start, pgoff_t end)
>> {
>> struct folio_batch fbatch;
>> pgoff_t next = start;
>> @@ -681,7 +681,7 @@ static void kvm_gmem_invalidate(struct inode *inode, pgoff_t start, pgoff_t end)
>> }
>> }
>> #else
>> -static void kvm_gmem_invalidate(struct inode *inode, pgoff_t start, pgoff_t end) {}
>> +static void kvm_gmem_make_shared(struct inode *inode, pgoff_t start, pgoff_t end) { }
>> #endif
>>
>> static int __kvm_gmem_set_attributes(struct inode *inode, pgoff_t start,
>> @@ -729,7 +729,7 @@ static int __kvm_gmem_set_attributes(struct inode *inode, pgoff_t start,
>> kvm_gmem_invalidate_start(inode, start, end);
>>
>> if (!to_private)
>> - kvm_gmem_invalidate(inode, start, end);
>> + kvm_gmem_make_shared(inode, start, end);
>>
>> mas_store_prealloc(&mas, xa_mk_value(attrs));
^ permalink raw reply
* Re: [PATCH v8 13/46] KVM: guest_memfd: Add base support for KVM_SET_MEMORY_ATTRIBUTES2
From: Ackerley Tng @ 2026-06-24 21:10 UTC (permalink / raw)
To: Binbin Wu
Cc: aik, andrew.jones, brauner, chao.p.peng, david, jmattson,
jthoughton, michael.roth, oupton, pankaj.gupta, qperret,
rick.p.edgecombe, rientjes, shivankg, steven.price, tabba, willy,
wyihan, yan.y.zhao, forkloop, pratyush, suzuki.poulose,
aneesh.kumar, liam, Paolo Bonzini, Sean Christopherson,
Thomas Gleixner, Ingo Molnar, Borislav Petkov, Dave Hansen, x86,
H. Peter Anvin, Steven Rostedt, Masami Hiramatsu,
Mathieu Desnoyers, Jonathan Corbet, Shuah Khan, Shuah Khan,
Vishal Annapurve, Andrew Morton, Chris Li, Kairui Song,
Kemeng Shi, Nhat Pham, Barry Song, Axel Rasmussen, Yuanchu Xie,
Wei Xu, Youngjun Park, Qi Zheng, Shakeel Butt, Kiryl Shutsemau,
Baoquan He, Jason Gunthorpe, Vlastimil Babka, kvm, linux-kernel,
linux-trace-kernel, linux-doc, linux-kselftest, linux-mm,
linux-coco
In-Reply-To: <ede86ac4-d560-49a6-82d6-b33ac5fc9355@linux.intel.com>
Binbin Wu <binbin.wu@linux.intel.com> writes:
> On 6/19/2026 8:31 AM, Ackerley Tng via B4 Relay wrote:
>> From: Ackerley Tng <ackerleytng@google.com>
>>
>> Introduce base support for KVM_SET_MEMORY_ATTRIBUTES2 in guest_memfd, which
>> just updates attributes tracked by guest_memfd.
>>
>> Validate input fields in general. Guard usage of KVM_SET_MEMORY_ATTRIBUTES2
>> by making sure requested attributes are supported for this instance of kvm.
>>
>> A new KVM_SET_MEMORY_ATTRIBUTES2 is defined to support writes (unlike
>> KVM_SET_MEMORY_ATTRIBUTES) in addition to reads so it can provide error
>> details to userspace. This will be used in a later patch.
>>
>> The two ioctls use their corresponding structs with no overlap, but
>> backward compatibility is baked in for future support of
>> KVM_SET_MEMORY_ATTRIBUTES2 and struct kvm_memory_attributes2 in the VM
>> ioctl.
>>
>> The process of setting memory attributes is set up such that the later half
>> will not fail due to allocation. Any necessary checks are performed before
>> the point of no return.
>>
>> Co-developed-by: Vishal Annapurve <vannapurve@google.com>
>> Signed-off-by: Vishal Annapurve <vannapurve@google.com>
>> Co-developed-by: Sean Christoperson <seanjc@google.com>
>> Signed-off-by: Sean Christoperson <seanjc@google.com>
>
> s/Christoperson /Christopherson
>
Thanks!
>> Reviewed-by: Fuad Tabba <tabba@google.com>
>> Signed-off-by: Ackerley Tng <ackerleytng@google.com>
>> ---
>> include/uapi/linux/kvm.h | 13 ++++++
>> virt/kvm/Kconfig | 1 +
>> virt/kvm/guest_memfd.c | 116 +++++++++++++++++++++++++++++++++++++++++++++++
>> virt/kvm/kvm_main.c | 12 +++++
>> 4 files changed, 142 insertions(+)
>>
>>
>
> [...]
>
>> diff --git a/virt/kvm/Kconfig b/virt/kvm/Kconfig
>> index 297e4399fbd49..cfa2c78ba5fb9 100644
>> --- a/virt/kvm/Kconfig
>> +++ b/virt/kvm/Kconfig
>> @@ -102,6 +102,7 @@ config KVM_MMU_LOCKLESS_AGING
>>
>> config KVM_GUEST_MEMFD
>> select XARRAY_MULTI
>> + select KVM_MEMORY_ATTRIBUTES
>
> What's this?
> This config is gone.
>
I'm surprised this compiles... I'll fix it, thanks!
>> bool
>>
^ permalink raw reply
* Re: [PATCH v8 13/46] KVM: guest_memfd: Add base support for KVM_SET_MEMORY_ATTRIBUTES2
From: Ackerley Tng @ 2026-06-24 21:03 UTC (permalink / raw)
To: Fuad Tabba, Sean Christopherson
Cc: aik, andrew.jones, binbin.wu, brauner, chao.p.peng, david,
jmattson, jthoughton, michael.roth, oupton, pankaj.gupta, qperret,
rick.p.edgecombe, rientjes, shivankg, steven.price, willy, wyihan,
yan.y.zhao, forkloop, pratyush, suzuki.poulose, aneesh.kumar,
liam, Paolo Bonzini, Thomas Gleixner, Ingo Molnar,
Borislav Petkov, Dave Hansen, x86, H. Peter Anvin, Steven Rostedt,
Masami Hiramatsu, Mathieu Desnoyers, Jonathan Corbet, Shuah Khan,
Shuah Khan, Vishal Annapurve, Andrew Morton, Chris Li,
Kairui Song, Kemeng Shi, Nhat Pham, Barry Song, Axel Rasmussen,
Yuanchu Xie, Wei Xu, Youngjun Park, Qi Zheng, Shakeel Butt,
Kiryl Shutsemau, Baoquan He, Jason Gunthorpe, Vlastimil Babka,
kvm, linux-kernel, linux-trace-kernel, linux-doc, linux-kselftest,
linux-mm, linux-coco
In-Reply-To: <CA+EHjTwLPCvZJgPv=8u3pgp+kwEwQbsXn_13FL3xUbJ7HRfXzw@mail.gmail.com>
Fuad Tabba <fuad.tabba@linux.dev> writes:
>
> [...snip...]
>
>> >
>> > Note sure if it's user error on my part, if I'm applying this to the
>> > wrong base, but I found a build break here on patch 13:
>> > kvm_gmem_invalidate_start() doesn't exist in the base tree. The
>> > function is kvm_gmem_invalidate_begin() here. The rename
>> > (190cc5370a8b6) landed via a different merge path and isn't an
>> > ancestor of the stated base.
>> >
>> > Patches 19 and 20 have the same mismatch. Fix for all three is
>> > s/kvm_gmem_invalidate_start/kvm_gmem_invalidate_begin/.
I took Sean's patches (off-list) and tried to combine it onto my
existing state. (I'm using b4 [1] to manage these series and I didn't
know I had to manually update the base-commit. Will try again next
revision.
[1] https://b4.docs.kernel.org/en/latest/
>>
>> Ya, Ackerley used a slightly older kvm/next to send the patches. I at least was
>> testing against kvm-x86/next, which does have the rename.
>>
>> Other than noting that this should be applied against the current kvm/next, I
>> don't think there's anything else to be done?
Should I base v9 on kvm/next, or kvm-x86/next?
>
> Agree. Sorry, didn't mean to be nit-picky, but this really threw me off :)
>
> Cheers,
> /fuad
^ permalink raw reply
* Re: [PATCH v8 10/46] KVM: guest_memfd: Wire up core private/shared attribute interfaces
From: Ackerley Tng @ 2026-06-24 20:44 UTC (permalink / raw)
To: Binbin Wu
Cc: aik, andrew.jones, brauner, chao.p.peng, david, jmattson,
jthoughton, michael.roth, oupton, pankaj.gupta, qperret,
rick.p.edgecombe, rientjes, shivankg, steven.price, tabba, willy,
wyihan, yan.y.zhao, forkloop, pratyush, suzuki.poulose,
aneesh.kumar, liam, Paolo Bonzini, Sean Christopherson,
Thomas Gleixner, Ingo Molnar, Borislav Petkov, Dave Hansen, x86,
H. Peter Anvin, Steven Rostedt, Masami Hiramatsu,
Mathieu Desnoyers, Jonathan Corbet, Shuah Khan, Shuah Khan,
Vishal Annapurve, Andrew Morton, Chris Li, Kairui Song,
Kemeng Shi, Nhat Pham, Barry Song, Axel Rasmussen, Yuanchu Xie,
Wei Xu, Youngjun Park, Qi Zheng, Shakeel Butt, Kiryl Shutsemau,
Baoquan He, Jason Gunthorpe, Vlastimil Babka, kvm, linux-kernel,
linux-trace-kernel, linux-doc, linux-kselftest, linux-mm,
linux-coco
In-Reply-To: <2ef455c3-a3f5-4ba1-86ea-b96416d163ce@linux.intel.com>
Binbin Wu <binbin.wu@linux.intel.com> writes:
> On 6/19/2026 8:31 AM, Ackerley Tng via B4 Relay wrote:
>
> [...]
>
>> diff --git a/virt/kvm/guest_memfd.c b/virt/kvm/guest_memfd.c
>> index bca912db5be6e..e0e544ef47d69 100644
>> --- a/virt/kvm/guest_memfd.c
>> +++ b/virt/kvm/guest_memfd.c
>> @@ -926,6 +926,24 @@ int kvm_gmem_get_pfn(struct kvm *kvm, struct kvm_memory_slot *slot,
>> EXPORT_SYMBOL_FOR_KVM_INTERNAL(kvm_gmem_get_pfn);
>>
>> #ifdef CONFIG_HAVE_KVM_ARCH_GMEM_POPULATE
>> +static bool kvm_gmem_range_is_private(struct file *file, pgoff_t index,
>> + size_t nr_pages, struct kvm *kvm, gfn_t gfn)
>> +{
>> + struct maple_tree *mt = &GMEM_I(file_inode(file))->attributes;
>> + pgoff_t end = index + nr_pages - 1;
>> + void *entry;
>> +
>> + if (!gmem_in_place_conversion)
>> + return kvm_range_has_vm_memory_attributes(kvm, gfn, gfn + nr_pages,
>> + KVM_MEMORY_ATTRIBUTE_PRIVATE,
>> + KVM_MEMORY_ATTRIBUTE_PRIVATE);
>> +
>> + mt_for_each(mt, entry, index, end) {
>> + if (xa_to_value(entry) != KVM_MEMORY_ATTRIBUTE_PRIVATE)
>> + return false;
>> + }
>
> Patch 1 noted that "Ensuring every index is represented in the maple tree at all times".
> So I think the queried range should not be a hole in the maple tree.
> However, there is a inconsistency: in patch 1 kvm_gmem_get_attributes() explicitly
> checks for holes, but this patch does not.
>
>> + return true;
>> +}
>>
With Sean's suggestion for patch 1, I'll update this one to default to
the "init" state if xa_to_value(entry) is NULL.
Thanks!
^ permalink raw reply
* Re: [PATCH] tracing/user_events: fix use-after-free of enabler in user_event_mm_dup()
From: Beau Belgrave @ 2026-06-24 20:05 UTC (permalink / raw)
To: XIAO WU
Cc: Michael Bommarito, Steven Rostedt, Masami Hiramatsu,
Mathieu Desnoyers, linux-trace-kernel, linux-kernel, stable
In-Reply-To: <tencent_89647CE40DC452B891C65C94D1B271DE8E07@qq.com>
On Tue, Jun 23, 2026 at 01:03:59AM +0800, XIAO WU wrote:
> Hi,
>
Hey XIAO WU,
> I came across the Sashiko AI review [1] in this thread and wanted to
> share some test results that may be useful.
>
Thanks!
> First — thank you for this patch! The enabler UAF in
> user_event_mm_dup() is a real bug and the fix (kfree → kfree_rcu) is
> the right approach for protecting the RCU list walkers. The selftest
> results you included in the commit are also really helpful.
>
> However, I was able to reproduce a second UAF on the *user_event*
> object that the Sashiko review flagged — it's still reachable after the
> patch is applied. I've included a PoC and crash log below.
>
> On Thu, Jun 18, 2026 at 06:27:43PM -0400, Michael Bommarito wrote:
> > @@ -404,7 +407,12 @@ static void user_event_enabler_destroy(struct
> user_event_enabler *enabler,
> > /* No longer tracking the event via the enabler */
> > user_event_put(enabler->event, locked);
> >
> > - kfree(enabler);
> > + /*
> > + * The enabler is removed from an RCU-traversed list
> > + * (user_event_mm_dup walks mm->enablers under rcu_read_lock only),
> > + * so the backing memory must outlive a grace period.
> > + */
> > + kfree_rcu(enabler, rcu);
> > }
>
> The issue: user_event_put(enabler->event, locked) is called
> synchronously, before kfree_rcu(enabler, rcu). If this drops the last
> reference to the user_event, delayed_destroy_user_event() is scheduled
> on a workqueue, which calls destroy_user_event() → kfree(user). The
> user_event memory is freed without RCU protection.
>
> But the enabler itself is now protected by kfree_rcu — it remains
> visible to RCU readers in user_event_mm_dup() during fork(). Those
> readers access enabler->event (via user_event_enabler_dup →
> user_event_get(orig->event)), which now points to freed memory:
>
> fork() unregister
> ──────── ──────────
> user_event_mm_dup()
> rcu_read_lock();
> list_for_each_entry_rcu(enabler, ...)
> user_event_enabler_destroy()
> list_del_rcu(enabler)
> user_event_put(enabler->event)
> → last ref!
> → schedule_work(put_work)
> kfree_rcu(enabler, rcu)
> user_event_enabler_dup(enabler, ...) [workqueue]
> enabler->event = delayed_destroy_user_event()
> user_event_get(orig->event); destroy_user_event()
> ↑ UAF: orig->event was freed! kfree(user_event)
>
While I cannot repro this locally on my 16 core machine, I do agree this
case needs to be handled correctly. The enabler should keep the ref to
the user_event until after an RCU grace period. I have this fix that
addresses it more completely than the original proposal.
I'm hoping you can try out this fix with your machine that does repro
the timing window. The below change needs self test fixes, since now the
free happens after an RCU grace period + work queue schedule. This is
because the self tests (abi_test and perf_test) assume after unreg the
last ref is immediate (which was never guaranteed).
Thanks,
-Beau
diff --git a/kernel/trace/trace_events_user.c b/kernel/trace/trace_events_user.c
index c4ba484f7b38..b860d8b70c7b 100644
--- a/kernel/trace/trace_events_user.c
+++ b/kernel/trace/trace_events_user.c
@@ -109,6 +109,9 @@ struct user_event_enabler {
/* Track enable bit, flags, etc. Aligned for bitops. */
unsigned long values;
+
+ /* Defer put so RCU list readers (user_event_mm_dup) are safe. */
+ struct rcu_work put_rwork;
};
/* Bits 0-5 are for the bit to update upon enable/disable (0-63 allowed) */
@@ -396,17 +399,38 @@ static struct user_event_group *user_event_group_create(void)
return NULL;
};
-static void user_event_enabler_destroy(struct user_event_enabler *enabler,
- bool locked)
+static void delayed_user_event_enabler_put(struct work_struct *work)
{
- list_del_rcu(&enabler->mm_enablers_link);
+ struct user_event_enabler *enabler;
+
+ enabler = container_of(to_rcu_work(work), struct user_event_enabler, put_rwork);
/* No longer tracking the event via the enabler */
- user_event_put(enabler->event, locked);
+ user_event_put(enabler->event, false);
+ /* Run from queue_rcu_work(), no need for RCU */
kfree(enabler);
}
+static void user_event_enabler_destroy(struct user_event_enabler *enabler)
+{
+ list_del_rcu(&enabler->mm_enablers_link);
+
+ /*
+ * We need to hold onto the reference of the user_event for this enabler
+ * until an RCU grace period has elapsed. This ensures that we only ever
+ * put (which may free) the user_event after all CPUs have an updated
+ * enabler list. If during the RCU grace period more enablers are added,
+ * the user_event will be kept alive by new ref counts.
+ *
+ * If user_event_put() is called on the last reference, the event_mutex
+ * is taken. These cannot be taken in an RCU context, so we have to run
+ * this in a work queue only after an RCU grace period.
+ */
+ INIT_RCU_WORK(&enabler->put_rwork, delayed_user_event_enabler_put);
+ queue_rcu_work(system_percpu_wq, &enabler->put_rwork);
+}
+
static int user_event_mm_fault_in(struct user_event_mm *mm, unsigned long uaddr,
int attempt)
{
@@ -464,7 +488,7 @@ static void user_event_enabler_fault_fixup(struct work_struct *work)
/* User asked for enabler to be removed during fault */
if (test_bit(ENABLE_VAL_FREEING_BIT, ENABLE_BITOPS(enabler))) {
- user_event_enabler_destroy(enabler, true);
+ user_event_enabler_destroy(enabler);
goto out;
}
@@ -764,7 +788,7 @@ static void user_event_mm_destroy(struct user_event_mm *mm)
struct user_event_enabler *enabler, *next;
list_for_each_entry_safe(enabler, next, &mm->enablers, mm_enablers_link)
- user_event_enabler_destroy(enabler, false);
+ user_event_enabler_destroy(enabler);
mmdrop(mm->mm);
kfree(mm);
@@ -2645,7 +2669,7 @@ static long user_events_ioctl_unreg(unsigned long uarg)
flags |= enabler->values & ENABLE_VAL_COMPAT_MASK;
if (!test_bit(ENABLE_VAL_FAULTING_BIT, ENABLE_BITOPS(enabler)))
- user_event_enabler_destroy(enabler, true);
+ user_event_enabler_destroy(enabler);
/* Removed at least one */
ret = 0;
^ permalink raw reply related
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