From: Sean Christopherson <sean.j.christopherson@intel.com>
To: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>,
Vitaly Kuznetsov <vkuznets@redhat.com>,
Wanpeng Li <wanpengli@tencent.com>,
Jim Mattson <jmattson@google.com>, Joerg Roedel <joro@8bytes.org>,
kvm@vger.kernel.org, linux-kernel@vger.kernel.org,
Uros Bizjak <ubizjak@gmail.com>, Andi Kleen <ak@linux.intel.com>
Subject: Re: [PATCH 1/2] KVM: VMX: Move IRQ invocation to assembly subroutine
Date: Mon, 14 Sep 2020 14:54:11 -0700 [thread overview]
Message-ID: <20200914215411.GF7192@sjchrist-ice> (raw)
In-Reply-To: <20200914213813.zfxlffphcp5czvof@treble>
On Mon, Sep 14, 2020 at 04:38:13PM -0500, Josh Poimboeuf wrote:
> On Mon, Sep 14, 2020 at 02:07:19PM -0700, Sean Christopherson wrote:
> > > RSP needs to be aligned to what? How would this align the stack, other
> > > than by accident?
> >
> > Ah, yeah, that's lacking info.
> >
> > 16-byte aligned to correctly mimic CPU behavior when vectoring an IRQ/NMI.
> > When not changing stack, the CPU aligns RSP before pushing the frame.
> >
> > The above shenanigans work because the x86-64 ABI also requires RSP to be
> > 16-byte aligned prior to CALL. RSP is thus 8-byte aligned due to CALL
> > pushing the return IP, and so creating the stack frame by pushing RBP makes
> > it 16-byte aliagned again.
>
> As Uros mentioned, the kernel doesn't do this.
Argh, apparently I just got lucky with my compiles then. I added explicit
checks on RSP being properly aligned and thought that confirmed the kernel
played nice. Bummer.
next prev parent reply other threads:[~2020-09-14 21:54 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-09-14 19:56 [PATCH 0/2] KVM: VMX: Clean up IRQ/NMI handling Sean Christopherson
2020-09-14 19:56 ` [PATCH 2/2] KVM: VMX: Invoke NMI handler via indirect call instead of INTn Sean Christopherson
[not found] ` <20200914195634.12881-2-sean.j.christopherson@intel.com>
2020-09-14 20:37 ` [PATCH 1/2] KVM: VMX: Move IRQ invocation to assembly subroutine Uros Bizjak
2020-09-14 21:08 ` Sean Christopherson
2020-09-14 20:40 ` Josh Poimboeuf
[not found] ` <20200914210719.GB7084@sjchrist-ice>
2020-09-14 21:21 ` Uros Bizjak
2020-09-14 21:31 ` Uros Bizjak
2020-09-14 21:55 ` Sean Christopherson
2020-09-14 21:38 ` Josh Poimboeuf
2020-09-14 21:54 ` Sean Christopherson [this message]
2020-09-15 2:42 ` Andi Kleen
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