netdev - Re: [PATCH 03/12] x86/xen: Introduce new function to map HYPERVISOR_shared

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Message-ID: <20200604230307.GB25251@dev-dsk-anchalag-2a-9c2d1d96.us-west-2.amazon.com>
Date:   Thu, 4 Jun 2020 23:03:07 +0000
From:   Anchal Agarwal <anchalag@...zon.com>
To:     Boris Ostrovsky <boris.ostrovsky@...cle.com>
CC:     <tglx@...utronix.de>, <mingo@...hat.com>, <bp@...en8.de>,
        <hpa@...or.com>, <x86@...nel.org>, <jgross@...e.com>,
        <linux-pm@...r.kernel.org>, <linux-mm@...ck.org>,
        <kamatam@...zon.com>, <sstabellini@...nel.org>,
        <konrad.wilk@...cle.com>, <roger.pau@...rix.com>,
        <axboe@...nel.dk>, <davem@...emloft.net>, <rjw@...ysocki.net>,
        <len.brown@...el.com>, <pavel@....cz>, <peterz@...radead.org>,
        <eduval@...zon.com>, <sblbir@...zon.com>,
        <xen-devel@...ts.xenproject.org>, <vkuznets@...hat.com>,
        <netdev@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <dwmw@...zon.co.uk>, <benh@...nel.crashing.org>
Subject: Re: [PATCH 03/12] x86/xen: Introduce new function to map
 HYPERVISOR_shared_info on Resume

On Sat, May 30, 2020 at 07:02:01PM -0400, Boris Ostrovsky wrote:
> CAUTION: This email originated from outside of the organization. Do not click links or open attachments unless you can confirm the sender and know the content is safe.
> 
> 
> 
> On 5/19/20 7:25 PM, Anchal Agarwal wrote:
> > Introduce a small function which re-uses shared page's PA allocated
> > during guest initialization time in reserve_shared_info() and not
> > allocate new page during resume flow.
> > It also  does the mapping of shared_info_page by calling
> > xen_hvm_init_shared_info() to use the function.
> >
> > Signed-off-by: Anchal Agarwal <anchalag@...zon.com>
> > ---
> >  arch/x86/xen/enlighten_hvm.c | 7 +++++++
> >  arch/x86/xen/xen-ops.h       | 1 +
> >  2 files changed, 8 insertions(+)
> >
> > diff --git a/arch/x86/xen/enlighten_hvm.c b/arch/x86/xen/enlighten_hvm.c
> > index e138f7de52d2..75b1ec7a0fcd 100644
> > --- a/arch/x86/xen/enlighten_hvm.c
> > +++ b/arch/x86/xen/enlighten_hvm.c
> > @@ -27,6 +27,13 @@
> >
> >  static unsigned long shared_info_pfn;
> >
> > +void xen_hvm_map_shared_info(void)
> > +{
> > +     xen_hvm_init_shared_info();
> > +     if (shared_info_pfn)
> > +             HYPERVISOR_shared_info = __va(PFN_PHYS(shared_info_pfn));
> > +}
> > +
> 
> 
> AFAICT it is only called once so I don't see a need for new routine.
> 
> 
HYPERVISOR_shared_info can only be mapped in this scope without refactoring
much of the code.
> And is it possible for shared_info_pfn to be NULL in resume path (which
> is where this is called)?
> 
> 
I don't think it should be, still a sanity check but I don't think its needed there
because hibernation will fail in any case if thats the case. 
However, HYPERVISOR_shared_info does needs to be re-mapped on resume as its been
marked to dummy address on suspend. Its also safe in case va changes.
Does the answer your question?
> -boris

-Anchal
> 
>