linux-kernel - Re: [PATCH v9 0/7] KVM: x86: Allow Qemu/KVM to use PVH entry point

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Date:   Thu, 13 Dec 2018 14:15:54 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Borislav Petkov <bp@...en8.de>,
        Maran Wilson <maran.wilson@...cle.com>
Cc:     x86@...nel.org, xen-devel@...ts.xenproject.org,
        linux-kernel@...r.kernel.org, kvm@...r.kernel.org, jgross@...e.com,
        boris.ostrovsky@...cle.com, bp@...e.de,
        dave.hansen@...ux.intel.com, davem@...emloft.net,
        gregkh@...uxfoundation.org, hpa@...or.com, jpoimboe@...hat.com,
        kirill.shutemov@...ux.intel.com, luto@...nel.org,
        mchehab@...nel.org, mingo@...hat.com, rdunlap@...radead.org,
        tglx@...utronix.de, thomas.lendacky@....com, hch@...radead.org,
        roger.pau@...rix.com, rkrcmar@...hat.com
Subject: Re: [PATCH v9 0/7] KVM: x86: Allow Qemu/KVM to use PVH entry point

On 12/12/18 21:39, Borislav Petkov wrote:
> On Tue, Dec 11, 2018 at 11:29:21AM -0800, Maran Wilson wrote:
>> Is your question about what options you need to provide to Qemu? Or is your
>> question about the SW implementation choices?
>>
>> Assuming the former...
> Yeah, that's what I wanted to know. But looking at it, I'm booting
> bzImage here just as quickly and as flexible so I don't see the
> advantage of this new method for my use case here of booting kernels
> in qemu.

It's not firmware that is slow, decompression is.  Unlike Xen, which is
using PVH with a regular bzImage and decompression in the host, KVM is
using PVH to boot a vmlinux with no decompression at all.

Paolo

> But maybe there's a good use case where firmware is slow and one doesn't
> really wanna noodle through it or when one does start a gazillion VMs
> per second or whatever...