From: Jork Loeser <jloeser@linux.microsoft.com>
To: Anirudh Rayabharam <anirudh@anirudhrb.com>
Cc: linux-hyperv@vger.kernel.org, x86@kernel.org,
"K . Y . Srinivasan" <kys@microsoft.com>,
Haiyang Zhang <haiyangz@microsoft.com>,
Wei Liu <wei.liu@kernel.org>, Dexuan Cui <decui@microsoft.com>,
Long Li <longli@microsoft.com>,
Thomas Gleixner <tglx@kernel.org>,
Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
Dave Hansen <dave.hansen@linux.intel.com>,
"H . Peter Anvin" <hpa@zytor.com>, Arnd Bergmann <arnd@arndb.de>,
Michael Kelley <mhklinux@outlook.com>,
linux-kernel@vger.kernel.org, linux-arch@vger.kernel.org
Subject: Re: [PATCH v2 4/6] mshv: limit SynIC management to MSHV-owned resources
Date: Tue, 7 Apr 2026 14:27:52 -0700 (PDT) [thread overview]
Message-ID: <134ce833-544-24eb-883-b190a888b31c@linux.microsoft.com> (raw)
In-Reply-To: <20260406-ninja-civet-of-tornado-67ff54@anirudhrb>
On Mon, 6 Apr 2026, Anirudh Rayabharam wrote:
> On Fri, Apr 03, 2026 at 12:06:10PM -0700, Jork Loeser wrote:
>> The SynIC is shared between VMBus and MSHV. VMBus owns the message
>> page (SIMP), event flags page (SIEFP), global enable (SCONTROL),
>> and SINT2. MSHV adds SINT0, SINT5, and the event ring page (SIRBP).
>>
>> Currently mshv_synic_init() redundantly enables SIMP, SIEFP, and
>
> The redundant enable is probably a no-op from the hypervisor side so it
> probably doesn't hurt us. The main problem is with the tear down.
It's an MSR intercept. If we can replace this by an "if()" we shave a few
cycles.
> An alternative approach could be: check if SIMP/SIEFP/SCONTROL is
> already enabled. If so, don't enable it again. If not enabled, enable it
> and keep track of what all stuf we have enabled. Then disable all of
> them during cleanup. This approach makes less assumptions about the
> behavior of the VMBUS driver and what stuff it does or doesn't use.
It would, yes. Then again, we drag yet more state and make debugging more
complicated / less clear to reason what happens dynamically. I had been
debating this briefly myself, and ultimately decided against it for that
very reason.
Best,
Jork
next prev parent reply other threads:[~2026-04-07 21:27 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-04-03 19:06 [PATCH v2 0/6] Hyper-V: kexec fixes for L1VH (mshv) Jork Loeser
2026-04-03 19:06 ` [PATCH v2 1/6] Drivers: hv: vmbus: fix hyperv_cpuhp_online variable shadowing Jork Loeser
2026-04-03 19:06 ` [PATCH v2 2/6] x86/hyperv: move stimer cleanup to hv_machine_shutdown() Jork Loeser
2026-04-03 19:06 ` [PATCH v2 3/6] x86/hyperv: Skip LP/VP creation on kexec Jork Loeser
2026-04-03 19:06 ` [PATCH v2 4/6] mshv: limit SynIC management to MSHV-owned resources Jork Loeser
2026-04-06 17:18 ` Anirudh Rayabharam
2026-04-07 21:27 ` Jork Loeser [this message]
2026-04-03 19:06 ` [PATCH v2 5/6] mshv: clean up SynIC state on kexec for L1VH Jork Loeser
2026-04-06 17:22 ` Anirudh Rayabharam
2026-04-03 19:06 ` [PATCH v2 6/6] mshv: unmap debugfs stats pages on kexec Jork Loeser
2026-04-06 17:28 ` Anirudh Rayabharam
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