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Re: [Qemu-devel] [PATCH v2 5/8] kvmvapic: Introduce TPR access optimizat
From: |
Gleb Natapov |
Subject: |
Re: [Qemu-devel] [PATCH v2 5/8] kvmvapic: Introduce TPR access optimization for Windows guests |
Date: |
Mon, 13 Feb 2012 21:11:56 +0200 |
On Mon, Feb 13, 2012 at 06:50:08PM +0000, Blue Swirl wrote:
> On Mon, Feb 13, 2012 at 10:16, Jan Kiszka <address@hidden> wrote:
> > On 2012-02-11 16:25, Blue Swirl wrote:
> >> On Fri, Feb 10, 2012 at 18:31, Jan Kiszka <address@hidden> wrote:
> >>> This enables acceleration for MMIO-based TPR registers accesses of
> >>> 32-bit Windows guest systems. It is mostly useful with KVM enabled,
> >>> either on older Intel CPUs (without flexpriority feature, can also be
> >>> manually disabled for testing) or any current AMD processor.
> >>>
> >>> The approach introduced here is derived from the original version of
> >>> qemu-kvm. It was refactored, documented, and extended by support for
> >>> user space APIC emulation, both with and without KVM acceleration. The
> >>> VMState format was kept compatible, so was the ABI to the option ROM
> >>> that implements the guest-side para-virtualized driver service. This
> >>> enables seamless migration from qemu-kvm to upstream or, one day,
> >>> between KVM and TCG mode.
> >>>
> >>> The basic concept goes like this:
> >>> - VAPIC PV interface consisting of I/O port 0x7e and (for KVM in-kernel
> >>> irqchip) a vmcall hypercall is registered
> >>> - VAPIC option ROM is loaded into guest
> >>> - option ROM activates TPR MMIO access reporting via port 0x7e
> >>> - TPR accesses are trapped and patched in the guest to call into option
> >>> ROM instead, VAPIC support is enabled
> >>> - option ROM TPR helpers track state in memory and invoke hypercall to
> >>> poll for pending IRQs if required
> >>>
> >>> Signed-off-by: Jan Kiszka <address@hidden>
> >>
> >> I must say that I find the approach horrible, patching guests and ROMs
> >> and looking up Windows internals. Taking the same approach to extreme,
> >> we could for example patch Xen guest to become a KVM guest. Not that I
> >> object merging.
> >
> > Yes, this is horrible. But there is no real better way in the absence of
> > hardware assisted virtualization of the TPR. I think MS is recommending
> > this patching approach as well.
>
> Maybe instead of routing via ROM and the hypercall, the TPR accesses
> could be handled directly with guest invisible breakpoints (like GDB
> breakpoints, but for QEMU internal use), much like other
> instrumentation could be handled.
>
Hypercall is rarely called. The idea behind patching is to not
have exit on each TPR update. Breakpoint will cause exit making the
whole exercise pointless.
--
Gleb.
- Re: [Qemu-devel] [PATCH v2 1/8] kvm: Set cpu_single_env only once, (continued)
- [Qemu-devel] [PATCH v2 6/8] kvmvapic: Simplify mp/up_set_tpr, Jan Kiszka, 2012/02/10
- [Qemu-devel] [PATCH v2 2/8] Allow to use pause_all_vcpus from VCPU context, Jan Kiszka, 2012/02/10
- [Qemu-devel] [PATCH v2 5/8] kvmvapic: Introduce TPR access optimization for Windows guests, Jan Kiszka, 2012/02/10
- Re: [Qemu-devel] [PATCH v2 5/8] kvmvapic: Introduce TPR access optimization for Windows guests, Blue Swirl, 2012/02/11
- Re: [Qemu-devel] [PATCH v2 5/8] kvmvapic: Introduce TPR access optimization for Windows guests, Jan Kiszka, 2012/02/13
- Re: [Qemu-devel] [PATCH v2 5/8] kvmvapic: Introduce TPR access optimization for Windows guests, Blue Swirl, 2012/02/13
- Re: [Qemu-devel] [PATCH v2 5/8] kvmvapic: Introduce TPR access optimization for Windows guests,
Gleb Natapov <=
- Re: [Qemu-devel] [PATCH v2 5/8] kvmvapic: Introduce TPR access optimization for Windows guests, Jan Kiszka, 2012/02/13
- Re: [Qemu-devel] [PATCH v2 5/8] kvmvapic: Introduce TPR access optimization for Windows guests, Gleb Natapov, 2012/02/14
- Re: [Qemu-devel] [PATCH v2 5/8] kvmvapic: Introduce TPR access optimization for Windows guests, Jan Kiszka, 2012/02/14
- Re: [Qemu-devel] [PATCH v2 5/8] kvmvapic: Introduce TPR access optimization for Windows guests, Gleb Natapov, 2012/02/14
[Qemu-devel] [PATCH v2 4/8] kvmvapic: Add option ROM, Jan Kiszka, 2012/02/10
[Qemu-devel] [PATCH v2 8/8] kvmvapic: Use optionrom helpers, Jan Kiszka, 2012/02/10