Date:   Wed, 27 May 2020 12:09:18 +0000
From:   Wei Liu <wei.liu@...nel.org>
To:     Boqun Feng <boqun.feng@...il.com>,
        Thomas Gleixner <tglx@...utronix.de>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        LKML <linux-kernel@...r.kernel.org>,
        Andy Lutomirski <luto@...nel.org>,
        Andrew Cooper <andrew.cooper3@...rix.com>,
        X86 ML <x86@...nel.org>,
        "Paul E. McKenney" <paulmck@...nel.org>,
        Alexandre Chartre <alexandre.chartre@...cle.com>,
        Frederic Weisbecker <frederic@...nel.org>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Petr Mladek <pmladek@...e.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Joel Fernandes <joel@...lfernandes.org>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Juergen Gross <jgross@...e.com>,
        Brian Gerst <brgerst@...il.com>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Will Deacon <will@...nel.org>,
        Tom Lendacky <thomas.lendacky@....com>,
        Wei Liu <wei.liu@...nel.org>,
        Michael Kelley <mikelley@...rosoft.com>,
        Jason Chen CJ <jason.cj.chen@...el.com>,
        Zhao Yakui <yakui.zhao@...el.com>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>
Subject: Re: [patch V9 30/39] x86/entry: Convert various hypervisor vectors
 to IDTENTRY_SYSVEC

On Wed, May 27, 2020 at 09:38:03AM +0100, Wei Liu wrote:
> On Wed, May 27, 2020 at 09:46:16AM +0800, Boqun Feng wrote:
> > Hi Thomas,
> > 
> > On Thu, May 21, 2020 at 10:05:43PM +0200, Thomas Gleixner wrote:
> > > From: Thomas Gleixner <tglx@...utronix.de>
> > > 
> > > Convert various hypervisor vectors to IDTENTRY_SYSVEC
> > >   - Implement the C entry point with DEFINE_IDTENTRY_SYSVEC
> > >   - Emit the ASM stub with DECLARE_IDTENTRY_SYSVEC
> > >   - Remove the ASM idtentries in 64bit
> > >   - Remove the BUILD_INTERRUPT entries in 32bit
> > >   - Remove the old prototypes
> > > 
> > > No functional change.
> > > 
> > > Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
> > > Acked-by: Andy Lutomirski <luto@...nel.org>
> > 
> > I hit the following while trying to test the whole patchset on a Hyper-V
> > guest, and git bisect told me this patch introduced the problem, the
> > config file is in the attachment.
> > 
> > Regards,
> > Boqun
> > 
> 
> Hi Boqun,
> 
> Thanks for testing and reporting.
> 
> This patch modifies Hyper-V's entry point so no wonder you pin down this
> patch.
> 
> > [    3.366637] BUG: kernel NULL pointer dereference, address: 0000000000000010
> > [    3.369959] #PF: supervisor instruction fetch in kernel mode
> > [    3.369959] #PF: error_code(0x0010) - not-present page
> > [    3.369959] PGD 0 P4D 0
> > [    3.369959] Oops: 0010 [#1] PREEMPT SMP PTI
> > [    3.369959] CPU: 27 PID: 0 Comm: swapper/27 Not tainted 5.7.0-rc5-00374-ge2d215d23d72 #23
> > [    3.369959] Hardware name: Microsoft Corporation Virtual Machine/Virtual Machine, BIOS Hyper-V UEFI Release v4.0 05/16/2019
> > [    3.369959] RIP: 0010:0x10
> 
> Hmmm... NULL pointer here.
> 
> > [    3.369959] Code: Bad RIP value.
> > [    3.369959] RSP: 0000:ffffbf444018beb8 EFLAGS: 00010086
> > [    3.369959] RAX: 000000000000001b RBX: ffffa04620900000 RCX: 00000000c8aab6dc
> > [    3.369959] RDX: 0000000000000001 RSI: ffffffffb390feaf RDI: ffffffffb3919e60
> > [    3.369959] RBP: 000000000000001b R08: 0000000000000000 R09: 0000000000000101
> > [    3.369959] R10: 0000000000dda899 R11: 0000000001d417ad R12: 0000000000000000
> > [    3.369959] R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000
> > [    3.369959] FS:  0000000000000000(0000) GS:ffffa04627ac0000(0000) knlGS:0000000000000000
> > [    3.369959] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> > [    3.369959] CR2: ffffffffffffffe6 CR3: 000000101bcba002 CR4: 00000000003606e0
> > [    3.369959] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> > [    3.369959] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> > [    3.369959] Call Trace:
> > [    3.369959]  ? default_idle+0x1c/0x190
> > [    3.369959]  ? do_idle+0x1cd/0x230
> > [    3.369959]  ? cpu_startup_entry+0x19/0x20
> > [    3.369959]  ? secondary_startup_64+0xa4/0xb0
> 
> And I certainly didn't expect this.
> 
> > [    3.369959] Modules linked in: crc32c_intel hv_vmbus(+)
> 
> VMBus is being loaded. That gives me some clue.
> 
> I notice a hunk in the patch:
> 
> @@ -331,17 +327,19 @@ static void __init ms_hyperv_init_platfo
>         x86_platform.apic_post_init = hyperv_init;
>         hyperv_setup_mmu_ops();
>         /* Setup the IDT for hypervisor callback */
> -       alloc_intr_gate(HYPERVISOR_CALLBACK_VECTOR, hyperv_callback_vector);
> +       alloc_intr_gate(HYPERVISOR_CALLBACK_VECTOR, sysvec_hyperv_callback);
> 
> It is not using the asm variant.
> 
> Could this be the culprit? Thomas?
> 

I'm able to reproduce the issue locally.  And after applying the
following diff I'm able to get a VM booting again on Hyper-V.

diff --git a/arch/x86/kernel/cpu/mshyperv.c b/arch/x86/kernel/cpu/mshyperv.c
index a103e1c0b90e..af94f05a5c66 100644
--- a/arch/x86/kernel/cpu/mshyperv.c
+++ b/arch/x86/kernel/cpu/mshyperv.c
@@ -327,7 +327,7 @@ static void __init ms_hyperv_init_platform(void)
        x86_platform.apic_post_init = hyperv_init;
        hyperv_setup_mmu_ops();
        /* Setup the IDT for hypervisor callback */
-       alloc_intr_gate(HYPERVISOR_CALLBACK_VECTOR, sysvec_hyperv_callback);
+       alloc_intr_gate(HYPERVISOR_CALLBACK_VECTOR, asm_sysvec_hyperv_callback);

        /* Setup the IDT for reenlightenment notifications */
        if (ms_hyperv.features & HV_X64_ACCESS_REENLIGHTENMENT) {

Boqun, can you give this a try?

Thomas, feel free to fold this in.

Wei.

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