linux-kernel - Re: [PATCH v2 3/4] KVM: x86: kvm_hv_flush

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Message-ID: <20210413090906.GA25751@u366d62d47e3651.ant.amazon.com>
Date:   Tue, 13 Apr 2021 11:09:41 +0200
From:   Siddharth Chandrasekaran <sidcha@...zon.de>
To:     Wei Liu <wei.liu@...nel.org>
CC:     "K. Y. Srinivasan" <kys@...rosoft.com>,
        Haiyang Zhang <haiyangz@...rosoft.com>,
        Stephen Hemminger <sthemmin@...rosoft.com>,
        "Thomas Gleixner" <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "Borislav Petkov" <bp@...en8.de>, <x86@...nel.org>,
        "H. Peter Anvin" <hpa@...or.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>,
        "Alexander Graf" <graf@...zon.com>,
        Evgeny Iakovlev <eyakovl@...zon.de>,
        Liran Alon <liran@...zon.com>,
        Ioannis Aslanidis <iaslan@...zon.de>,
        <linux-hyperv@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <kvm@...r.kernel.org>
Subject: Re: [PATCH v2 3/4] KVM: x86: kvm_hv_flush_tlb use inputs from XMM registers

On Mon, Apr 12, 2021 at 08:13:19PM +0000, Wei Liu wrote:
> On Mon, Apr 12, 2021 at 07:00:16PM +0200, Siddharth Chandrasekaran wrote:
> > +
> > +static inline void kvm_hv_hypercall_read_xmm(struct kvm_hv_hcall *hc)
> 
> Do you really need inline here? The compiler should be smart enough to
> inline this function if necessary.

Removed.

> > +{
> > +     int reg;
> > +
> > +     kvm_fpu_get();
> > +     for (reg = 0; reg < KVM_HV_HYPERCALL_MAX_XMM_REGISTERS; reg++)
> > +             _kvm_read_sse_reg(reg, &hc->xmm[reg]);
> > +     kvm_fpu_put();
> > +     hc->xmm_dirty = false;
> 
> There is no code that sets xmm_dirty to true? What am I missing? I guess
> that's because you haven't implemented the hypercalls that need writing
> back to guest?

Yes, when a hypercall want to return data via XMM registers, it should
update hc->xmm[] and set hc->dirty (I plan on using this in a future
patch). The reason why I didn't differ this change to actual patch
needs it is that it pairs nicely with the read/write xmm_reg() calls in
kvm_hv_hypercall().

~ Sid.



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