From: Anup Patel <anup@brainfault.org>
To: Paolo Bonzini <pbonzini@redhat.com>
Cc: Anup Patel <Anup.Patel@wdc.com>,
Palmer Dabbelt <palmer@sifive.com>,
Paul Walmsley <paul.walmsley@sifive.com>,
Radim K <rkrcmar@redhat.com>,
Daniel Lezcano <daniel.lezcano@linaro.org>,
Thomas Gleixner <tglx@linutronix.de>,
Atish Patra <Atish.Patra@wdc.com>,
Alistair Francis <Alistair.Francis@wdc.com>,
Damien Le Moal <Damien.LeMoal@wdc.com>,
Christoph Hellwig <hch@infradead.org>,
"kvm@vger.kernel.org" <kvm@vger.kernel.org>,
"linux-riscv@lists.infradead.org"
<linux-riscv@lists.infradead.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Re: [RFC PATCH 05/16] RISC-V: KVM: Implement VCPU interrupts and requests handling
Date: Tue, 30 Jul 2019 18:15:39 +0530 [thread overview]
Message-ID: <CAAhSdy3b-o6y1fsYi1iQcCN=9ZuC98TLCqjHCYAzOCx+N+_89w@mail.gmail.com> (raw)
In-Reply-To: <66c4e468-7a69-31e7-778b-228908f0e737@redhat.com>
On Tue, Jul 30, 2019 at 5:42 PM Paolo Bonzini <pbonzini@redhat.com> wrote:
>
> On 30/07/19 14:00, Anup Patel wrote:
> > On Tue, Jul 30, 2019 at 4:47 PM Paolo Bonzini <pbonzini@redhat.com> wrote:
> >>
> >> First, something that is not clear to me: how do you deal with a guest
> >> writing 1 to VSIP.SSIP? I think that could lead to lost interrupts if
> >> you have the following sequence
> >>
> >> 1) guest writes 1 to VSIP.SSIP
> >>
> >> 2) guest leaves VS-mode
> >>
> >> 3) host syncs VSIP
> >>
> >> 4) user mode triggers interrupt
> >>
> >> 5) host reenters guest
> >>
> >> 6) host moves irqs_pending to VSIP and clears VSIP.SSIP in the process
> >
> > This reasoning also apply to M-mode firmware (OpenSBI) providing timer
> > and IPI services to HS-mode software. We had some discussion around
> > it in a different context.
> > (Refer, https://github.com/riscv/opensbi/issues/128)
> >
> > The thing is SIP CSR is supposed to be read-only for any S-mode SW. This
> > means HS-mode/VS-mode SW modifications to SIP CSR should have no
> > effect.
>
> Is it? The privileged specification says
>
> Interprocessor interrupts are sent to other harts by implementation-
> specific means, which will ultimately cause the SSIP bit to be set in
> the recipient hart’s sip register.
To further explain my rationale ...
Here's some text from RISC-V spec regarding MIP CSR:
"The mip register is an MXLEN-bit read/write register containing information
on pending interrupts, while mie is the corresponding MXLEN-bit read/write
register containing interrupt enable bits. Only the bits corresponding to
lower-privilege software interrupts (USIP, SSIP), timer interrupts (UTIP, STIP),
and external interrupts (UEIP, SEIP) in mip are writable through this CSR
address; the remaining bits are read-only."
Here's some text from RISC-V spec regarding SIP CSR:
"software interrupt-pending (SSIP) bit in the sip register. A pending
supervisor-level software interrupt can be cleared by writing 0 to the SSIP bit
in sip. Supervisor-level software interrupts are disabled when the SSIE bit in
the sie register is clear."
Without RISC-V hypervisor extension, the SIP is essentially a restricted
view of MIP CSR. Also as-per above, S-mode SW can only write 0 to SSIP
bit in SIP CSR whereas it can only be set by M-mode SW or some HW
mechanism (such as S-mode CLINT).
There was quite a bit of discussion in last RISC-V Zurich Workshop about
avoiding SBI calls for injecting IPIs. The best suggestion so far is to
eventually have RISC-V systems with separate CLINT HW for M-mode
and S-mode. The S-mode SW can use S-mode CLINT to trigger IPIs to
other CPUs and it will use SBI calls for IPIs only when S-mode CLINT is
not available.
>
> All bits besides SSIP in the sip register are read-only.
>
> Meaning that sending an IPI to self by writing 1 to sip.SSIP is
> well-defined. The same should be true of vsip.SSIP while in VS mode.
>
> > Do you still an issue here?
>
> Do you see any issues in the pseudocode I sent? It gets away with the
> spinlock and request so it may be a good idea anyway. :)
Yes, I am evaluating your psedocode right now. I definitely want to
remove the irq_pending_lock if possible. I will try to in-corporate your
suggestion in v2 series.
Regards,
Anup
next prev parent reply other threads:[~2019-07-30 12:45 UTC|newest]
Thread overview: 67+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-07-29 11:56 [RFC PATCH 00/16] KVM RISC-V Support Anup Patel
2019-07-29 11:56 ` [RFC PATCH 01/16] KVM: RISC-V: Add KVM_REG_RISCV for ONE_REG interface Anup Patel
2019-07-29 11:56 ` [RFC PATCH 02/16] RISC-V: Add hypervisor extension related CSR defines Anup Patel
2019-07-29 11:56 ` [RFC PATCH 03/16] RISC-V: Add initial skeletal KVM support Anup Patel
2019-07-30 9:23 ` Paolo Bonzini
2019-07-30 11:04 ` Anup Patel
2019-07-30 9:25 ` Paolo Bonzini
2019-07-30 11:03 ` Anup Patel
2019-07-29 11:56 ` [RFC PATCH 04/16] RISC-V: KVM: Implement VCPU create, init and destroy functions Anup Patel
2019-07-30 8:48 ` Paolo Bonzini
2019-07-30 10:16 ` Paolo Bonzini
2019-07-30 11:45 ` Anup Patel
2019-07-30 11:47 ` Paolo Bonzini
2019-07-29 11:56 ` [RFC PATCH 05/16] RISC-V: KVM: Implement VCPU interrupts and requests handling Anup Patel
2019-07-30 11:17 ` Paolo Bonzini
2019-07-30 12:00 ` Anup Patel
2019-07-30 12:12 ` Paolo Bonzini
2019-07-30 12:45 ` Anup Patel [this message]
2019-07-30 13:18 ` Paolo Bonzini
2019-07-30 13:35 ` Anup Patel
2019-07-30 14:08 ` Paolo Bonzini
2019-08-02 3:59 ` Anup Patel
2019-07-29 11:56 ` [RFC PATCH 06/16] RISC-V: KVM: Implement KVM_GET_ONE_REG/KVM_SET_ONE_REG ioctls Anup Patel
2019-07-30 8:43 ` Paolo Bonzini
2019-07-30 9:35 ` Paolo Bonzini
2019-07-30 12:08 ` Anup Patel
2019-07-30 12:10 ` Paolo Bonzini
2019-07-30 12:16 ` Anup Patel
2019-07-29 11:57 ` [RFC PATCH 07/16] RISC-V: KVM: Implement VCPU world-switch Anup Patel
2019-07-30 9:34 ` Paolo Bonzini
2019-07-30 12:51 ` Anup Patel
2019-07-29 11:57 ` [RFC PATCH 08/16] RISC-V: KVM: Handle MMIO exits for VCPU Anup Patel
2019-07-30 11:20 ` Paolo Bonzini
2019-07-31 7:23 ` Anup Patel
2019-07-29 11:57 ` [RFC PATCH 09/16] RISC-V: KVM: Handle WFI " Anup Patel
2019-07-29 11:57 ` [RFC PATCH 10/16] RISC-V: KVM: Implement VMID allocator Anup Patel
2019-07-30 8:59 ` Paolo Bonzini
2019-07-29 11:57 ` [RFC PATCH 11/16] RISC-V: KVM: Implement stage2 page table programming Anup Patel
2019-07-30 9:00 ` Paolo Bonzini
2019-07-30 12:14 ` Anup Patel
2019-07-29 11:57 ` [RFC PATCH 12/16] RISC-V: KVM: Implement MMU notifiers Anup Patel
2019-07-29 11:57 ` [RFC PATCH 13/16] RISC-V: KVM: Add timer functionality Anup Patel
2019-07-29 14:40 ` Andreas Schwab
2019-07-29 18:02 ` Atish Patra
2019-07-30 6:51 ` Andreas Schwab
2019-07-30 7:00 ` Atish Patra
2019-07-30 11:26 ` Paolo Bonzini
2019-07-31 1:55 ` Atish Patra
2019-07-31 6:58 ` Paolo Bonzini
2019-07-31 7:18 ` Anup Patel
2019-07-29 11:57 ` [RFC PATCH 14/16] RISC-V: KVM: FP lazy save/restore Anup Patel
2019-07-29 11:57 ` [RFC PATCH 15/16] RISC-V: KVM: Add SBI v0.1 support Anup Patel
2019-07-29 19:40 ` Paolo Bonzini
2019-07-29 19:51 ` Atish Patra
2019-07-29 20:08 ` Paolo Bonzini
2019-07-29 21:08 ` Atish Patra
2019-07-30 9:26 ` Paolo Bonzini
2019-07-29 11:58 ` [RFC PATCH 16/16] RISC-V: Enable VIRTIO drivers in RV64 and RV32 defconfig Anup Patel
2019-07-29 21:47 ` [RFC PATCH 00/16] KVM RISC-V Support Paolo Bonzini
2019-07-30 5:26 ` Anup Patel
2019-07-30 11:33 ` Paolo Bonzini
2019-07-30 13:50 ` Anup Patel
2019-07-30 14:02 ` Paolo Bonzini
2019-07-30 6:53 ` Andreas Schwab
2019-07-30 7:25 ` Anup Patel
2019-07-30 7:42 ` Andreas Schwab
2019-07-30 7:36 ` Anup Patel
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