[PATCH] KVM: x86: User mutex guards to eliminate __kvm_x86_vendor_init()

[PATCH] KVM: x86: User mutex guards to eliminate __kvm_x86_vendor_init()

[Nikolay Borisov]

Current separation between (__){0,1}kvm_x86_vendor_init() is superfluos as
the the underscore version doesn't have any other callers.

Instead, use the newly added cleanup infrastructure to ensure that
kvm_x86_vendor_init() holds the vendor_module_lock throughout its
exectuion and that in case of error in the middle it's released. No
functional changes.

Signed-off-by: Nikolay Borisov <nik.borisov@suse.com>
---
 arch/x86/kvm/x86.c | 15 +++------------
 1 file changed, 3 insertions(+), 12 deletions(-)

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 41cce5031126..cd7c2d0f88cb 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -9446,11 +9446,13 @@ static void kvm_x86_check_cpu_compat(void *ret)
 	*(int *)ret = kvm_x86_check_processor_compatibility();
 }
 
-static int __kvm_x86_vendor_init(struct kvm_x86_init_ops *ops)
+int kvm_x86_vendor_init(struct kvm_x86_init_ops *ops)
 {
 	u64 host_pat;
 	int r, cpu;
 
+	guard(mutex)(&vendor_module_lock);
+
 	if (kvm_x86_ops.hardware_enable) {
 		pr_err("already loaded vendor module '%s'\n", kvm_x86_ops.name);
 		return -EEXIST;
@@ -9580,17 +9582,6 @@ static int __kvm_x86_vendor_init(struct kvm_x86_init_ops *ops)
 	kmem_cache_destroy(x86_emulator_cache);
 	return r;
 }
-
-int kvm_x86_vendor_init(struct kvm_x86_init_ops *ops)
-{
-	int r;
-
-	mutex_lock(&vendor_module_lock);
-	r = __kvm_x86_vendor_init(ops);
-	mutex_unlock(&vendor_module_lock);
-
-	return r;
-}
 EXPORT_SYMBOL_GPL(kvm_x86_vendor_init);
 
 void kvm_x86_vendor_exit(void)
-- 
2.34.1

Re: [PATCH] KVM: x86: User mutex guards to eliminate __kvm_x86_vendor_init()

[Sean Christopherson]

On Mon, Oct 30, 2023, Nikolay Borisov wrote:
> Current separation between (__){0,1}kvm_x86_vendor_init() is superfluos as

superfluous

But this intro is actively misleading.  The double-underscore variant most definitely
isn't superfluous, e.g. it eliminates the need for gotos reduces the probability
of incorrect error codes, bugs in the error handling, etc.  It _becomes_ superflous
after switching to guard(mutex).

IMO, this is one of the instances where the "problem, then solution" appoach is
counter-productive.  If there are no objections, I'll massage the change log to
the below when applying (for 6.8, in a few weeks).

  Use the recently introduced guard(mutex) infrastructure acquire and
  automatically release vendor_module_lock when the guard goes out of scope.
  Drop the inner __kvm_x86_vendor_init(), its sole purpose was to simplify
  releasing vendor_module_lock in error paths.

  No functional change intended.

> the the underscore version doesn't have any other callers.
> 
> Instead, use the newly added cleanup infrastructure to ensure that
> kvm_x86_vendor_init() holds the vendor_module_lock throughout its
> exectuion and that in case of error in the middle it's released. No
> functional changes.

Re: [PATCH] KVM: x86: User mutex guards to eliminate __kvm_x86_vendor_init()

[Nikolay Borisov]

On 30.10.23 г. 18:07 ч., Sean Christopherson wrote:
> On Mon, Oct 30, 2023, Nikolay Borisov wrote:
>> Current separation between (__){0,1}kvm_x86_vendor_init() is superfluos as
> 
> superfluous
> 
> But this intro is actively misleading.  The double-underscore variant most definitely
> isn't superfluous, e.g. it eliminates the need for gotos reduces the probability
> of incorrect error codes, bugs in the error handling, etc.  It _becomes_ superflous
> after switching to guard(mutex).
> 
> IMO, this is one of the instances where the "problem, then solution" appoach is
> counter-productive.  If there are no objections, I'll massage the change log to
> the below when applying (for 6.8, in a few weeks).
> 
>    Use the recently introduced guard(mutex) infrastructure acquire and
>    automatically release vendor_module_lock when the guard goes out of scope.
>    Drop the inner __kvm_x86_vendor_init(), its sole purpose was to simplify
>    releasing vendor_module_lock in error paths.
> 
>    No functional change intended.

Thanks, I'm fine with this changelog.

> 
>> the the underscore version doesn't have any other callers.
>>
>> Instead, use the newly added cleanup infrastructure to ensure that
>> kvm_x86_vendor_init() holds the vendor_module_lock throughout its
>> exectuion and that in case of error in the middle it's released. No
>> functional changes.
> 

Re: [PATCH] KVM: x86: User mutex guards to eliminate __kvm_x86_vendor_init()

[Paolo Bonzini]

On 10/30/23 17:07, Sean Christopherson wrote:
> On Mon, Oct 30, 2023, Nikolay Borisov wrote:
>> Current separation between (__){0,1}kvm_x86_vendor_init() is superfluos as
> 
> superfluous
> 
> But this intro is actively misleading.  The double-underscore variant most definitely
> isn't superfluous, e.g. it eliminates the need for gotos reduces the probability
> of incorrect error codes, bugs in the error handling, etc.  It _becomes_ superflous
> after switching to guard(mutex).
> 
> IMO, this is one of the instances where the "problem, then solution" appoach is
> counter-productive.  If there are no objections, I'll massage the change log to
> the below when applying (for 6.8, in a few weeks).

I think this is a "Speak Now or Forever Rest in Peace" situation.  I'm 
going to wait a couple days more for reviews to come in, post a v14 
myself, and apply the series to kvm/next as soon as Linus merges the 6.7 
changes.  The series will be based on the 6.7 tags/for-linus, and when 
6.7-rc1 comes up, I'll do this to straighten the history:

	git checkout kvm/next
	git tag -s -f kvm-gmem HEAD
	git reset --hard v6.7-rc1
	git merge tags/kvm-gmem
	# fix conflict with Christian Brauner's VFS series
	git commit
	git push kvm

6.8 is not going to be out for four months, and I'm pretty sure that 
anything discovered within "a few weeks" can be applied on top, and the 
heaviness of a 35-patch series will outweigh any imperfections by a long 
margin).

(Full disclosure: this is _also_ because I want to apply this series to 
the RHEL kernel, and Red Hat has a high level of disdain for 
non-upstream patches.  But it's mostly because I want all dependencies 
to be able to move on and be developed on top of stock kvm/next).

Paolo

Re: [PATCH] KVM: x86: User mutex guards to eliminate __kvm_x86_vendor_init()

[Sean Christopherson]

On Mon, Oct 30, 2023, Paolo Bonzini wrote:
> On 10/30/23 17:07, Sean Christopherson wrote:
> > On Mon, Oct 30, 2023, Nikolay Borisov wrote:
> > > Current separation between (__){0,1}kvm_x86_vendor_init() is superfluos as
> > 
> > superfluous
> > 
> > But this intro is actively misleading.  The double-underscore variant most definitely
> > isn't superfluous, e.g. it eliminates the need for gotos reduces the probability
> > of incorrect error codes, bugs in the error handling, etc.  It _becomes_ superflous
> > after switching to guard(mutex).
> > 
> > IMO, this is one of the instances where the then solution problem appoach is
> > counter-productive.  If there are no objections, I'll massage the change log to
> > the below when applying (for 6.8, in a few weeks).
> 
> I think this is a "Speak Now or Forever Rest in Peace" situation.  I'm going
> to wait a couple days more for reviews to come in, post a v14 myself, and
> apply the series to kvm/next as soon as Linus merges the 6.7 changes.  The
> series will be based on the 6.7 tags/for-linus, and when 6.7-rc1 comes up,
> I'll do this to straighten the history:

Heh, I'm pretty sure you meant to respond to the guest_memfd series.

> 	git checkout kvm/next
> 	git tag -s -f kvm-gmem HEAD
> 	git reset --hard v6.7-rc1
> 	git merge tags/kvm-gmem
> 	# fix conflict with Christian Brauner's VFS series
> 	git commit
> 	git push kvm
> 
> 6.8 is not going to be out for four months, and I'm pretty sure that
> anything discovered within "a few weeks" can be applied on top, and the
> heaviness of a 35-patch series will outweigh any imperfections by a long
> margin).
> 
> (Full disclosure: this is _also_ because I want to apply this series to the
> RHEL kernel, and Red Hat has a high level of disdain for non-upstream
> patches.  But it's mostly because I want all dependencies to be able to move
> on and be developed on top of stock kvm/next).

Re: [PATCH] KVM: x86: User mutex guards to eliminate __kvm_x86_vendor_init()

[Paolo Bonzini]

On 10/30/23 18:36, Sean Christopherson wrote:
>>> If there are no objections, I'll massage the change log to
>>> the below when applying (for 6.8, in a few weeks).
>>
>> I think this is a "Speak Now or Forever Rest in Peace" situation.  I'm going
>> to wait a couple days more for reviews to come in, post a v14 myself, and
>> apply the series to kvm/next as soon as Linus merges the 6.7 changes.  The
>> series will be based on the 6.7 tags/for-linus, and when 6.7-rc1 comes up,
>> I'll do this to straighten the history:
>
> Heh, I'm pretty sure you meant to respond to the guest_memfd series.

Well, it was the "in a few weeks" that almost caused me a panic attack. 
:)  But yeah, I soon got to the conclusion that this required a wider 
diffusion and reposted there.

Paolo

Re: [PATCH] KVM: x86: User mutex guards to eliminate __kvm_x86_vendor_init()

[Huang, Kai]

On Mon, 2023-10-30 at 18:17 +0200, Nikolay Borisov wrote:
> 
> On 30.10.23 г. 18:07 ч., Sean Christopherson wrote:
> > On Mon, Oct 30, 2023, Nikolay Borisov wrote:
> > > Current separation between (__){0,1}kvm_x86_vendor_init() is superfluos as
> > 
> > superfluous
> > 
> > But this intro is actively misleading.  The double-underscore variant most definitely
> > isn't superfluous, e.g. it eliminates the need for gotos reduces the probability
> > of incorrect error codes, bugs in the error handling, etc.  It _becomes_ superflous
> > after switching to guard(mutex).
> > 
> > IMO, this is one of the instances where the "problem, then solution" appoach is
> > counter-productive.  If there are no objections, I'll massage the change log to
> > the below when applying (for 6.8, in a few weeks).
> > 
> >    Use the recently introduced guard(mutex) infrastructure acquire and
> >    automatically release vendor_module_lock when the guard goes out of scope.
> >    Drop the inner __kvm_x86_vendor_init(), its sole purpose was to simplify
> >    releasing vendor_module_lock in error paths.
> > 
> >    No functional change intended.
> 
> Thanks, I'm fine with this changelog.
> 
> 

Reviewed-by: Kai Huang <kai.huang@intel.com>

Re: [PATCH] KVM: x86: User mutex guards to eliminate __kvm_x86_vendor_init()

[Nikolay Borisov]

On 30.10.23 г. 18:07 ч., Sean Christopherson wrote:
> On Mon, Oct 30, 2023, Nikolay Borisov wrote:
>> Current separation between (__){0,1}kvm_x86_vendor_init() is 
>> superfluos as
> 
> superfluous
> 
> But this intro is actively misleading.  The double-underscore variant 
> most definitely
> isn't superfluous, e.g. it eliminates the need for gotos reduces the 
> probability
> of incorrect error codes, bugs in the error handling, etc.  It _becomes_ 
> superflous
> after switching to guard(mutex).
> 
> IMO, this is one of the instances where the "problem, then solution" 
> appoach is
> counter-productive.  If there are no objections, I'll massage the change 
> log to
> the below when applying (for 6.8, in a few weeks).
> 
>   Use the recently introduced guard(mutex) infrastructure acquire and
>   automatically release vendor_module_lock when the guard goes out of 
> scope.
>   Drop the inner __kvm_x86_vendor_init(), its sole purpose was to simplify
>   releasing vendor_module_lock in error paths.
> 
>   No functional change intended.
> 
>> the the underscore version doesn't have any other callers.
>>


Has this fallen through the cracks as I don't see it in 6.7?

Re: [PATCH] KVM: x86: User mutex guards to eliminate __kvm_x86_vendor_init()

[Sean Christopherson]

On Sat, Dec 09, 2023, Nikolay Borisov wrote:
> 
> 
> On 30.10.23 г. 18:07 ч., Sean Christopherson wrote:
> > On Mon, Oct 30, 2023, Nikolay Borisov wrote:
> > > Current separation between (__){0,1}kvm_x86_vendor_init() is
> > > superfluos as
> > 
> > superfluous
> > 
> > But this intro is actively misleading.  The double-underscore variant
> > most definitely
> > isn't superfluous, e.g. it eliminates the need for gotos reduces the
> > probability
> > of incorrect error codes, bugs in the error handling, etc.  It _becomes_
> > superflous
> > after switching to guard(mutex).
> > 
> > IMO, this is one of the instances where the then solution problem
> > appoach is
> > counter-productive.  If there are no objections, I'll massage the change
> > log to
> > the below when applying (for 6.8, in a few weeks).
> > 
> >   Use the recently introduced guard(mutex) infrastructure acquire and
> >   automatically release vendor_module_lock when the guard goes out of
> > scope.
> >   Drop the inner __kvm_x86_vendor_init(), its sole purpose was to simplify
> >   releasing vendor_module_lock in error paths.
> > 
> >   No functional change intended.
> > 
> > > the the underscore version doesn't have any other callers.
> > > 
> 
> 
> Has this fallen through the cracks as I don't see it in 6.7?

As above, I have this tagged for inclusion in 6.8, not 6.7.  Though admittedly,
this one did actually fall through the cracks as I moved it to the wrong mailbox
when Paolo usurped the thread for unrelated guest_memfd stuff.  Anyways, I do
plan on grabbing this for 6.8, I'm just buried in non-upstream stuff right now.

Re: [PATCH] KVM: x86: User mutex guards to eliminate __kvm_x86_vendor_init()

[Sean Christopherson]

On Mon, 30 Oct 2023 16:17:28 +0200, Nikolay Borisov wrote:
> Current separation between (__){0,1}kvm_x86_vendor_init() is superfluos as
> the the underscore version doesn't have any other callers.
> 
> Instead, use the newly added cleanup infrastructure to ensure that
> kvm_x86_vendor_init() holds the vendor_module_lock throughout its
> exectuion and that in case of error in the middle it's released. No
> functional changes.
> 
> [...]

Applied to kvm-x86 misc, thanks!

[1/1] KVM: x86: Use mutex guards to eliminate __kvm_x86_vendor_init()
      https://github.com/kvm-x86/linux/commit/955997e88017

--
https://github.com/kvm-x86/linux/tree/next