linux-kernel - Re: [PATCH RFC v1 06/18] x86/hyperv: allocate output arg pages if required

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Date:   Tue, 15 Sep 2020 12:43:18 +0000
From:   Wei Liu <wei.liu@...nel.org>
To:     Vitaly Kuznetsov <vkuznets@...hat.com>
Cc:     Wei Liu <wei.liu@...nel.org>,
        Linux on Hyper-V List <linux-hyperv@...r.kernel.org>,
        virtualization@...ts.linux-foundation.org,
        Linux Kernel List <linux-kernel@...r.kernel.org>,
        Michael Kelley <mikelley@...rosoft.com>,
        Vineeth Pillai <viremana@...ux.microsoft.com>,
        Sunil Muthuswamy <sunilmut@...rosoft.com>,
        Nuno Das Neves <nudasnev@...rosoft.com>,
        Lillian Grassin-Drake <ligrassi@...rosoft.com>,
        "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>,
        "maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)" <x86@...nel.org>,
        "H. Peter Anvin" <hpa@...or.com>
Subject: Re: [PATCH RFC v1 06/18] x86/hyperv: allocate output arg pages if
 required

On Tue, Sep 15, 2020 at 12:16:58PM +0200, Vitaly Kuznetsov wrote:
> Wei Liu <wei.liu@...nel.org> writes:
> 
> > When Linux runs as the root partition, it will need to make hypercalls
> > which return data from the hypervisor.
> >
> > Allocate pages for storing results when Linux runs as the root
> > partition.
> >
> > Signed-off-by: Lillian Grassin-Drake <ligrassi@...rosoft.com>
> > Co-Developed-by: Lillian Grassin-Drake <ligrassi@...rosoft.com>
> > Signed-off-by: Wei Liu <wei.liu@...nel.org>
> > ---
> >  arch/x86/hyperv/hv_init.c       | 45 +++++++++++++++++++++++++++++----
> >  arch/x86/include/asm/mshyperv.h |  1 +
> >  2 files changed, 41 insertions(+), 5 deletions(-)
> >
> > diff --git a/arch/x86/hyperv/hv_init.c b/arch/x86/hyperv/hv_init.c
> > index cac8e4c56261..ebba4be4185d 100644
> > --- a/arch/x86/hyperv/hv_init.c
> > +++ b/arch/x86/hyperv/hv_init.c
> > @@ -45,6 +45,9 @@ EXPORT_SYMBOL_GPL(hv_vp_assist_page);
> >  void  __percpu **hyperv_pcpu_input_arg;
> >  EXPORT_SYMBOL_GPL(hyperv_pcpu_input_arg);
> >  
> > +void  __percpu **hyperv_pcpu_output_arg;
> > +EXPORT_SYMBOL_GPL(hyperv_pcpu_output_arg);
> > +
> >  u32 hv_max_vp_index;
> >  EXPORT_SYMBOL_GPL(hv_max_vp_index);
> >  
> > @@ -75,14 +78,29 @@ static int hv_cpu_init(unsigned int cpu)
> >  	u64 msr_vp_index;
> >  	struct hv_vp_assist_page **hvp = &hv_vp_assist_page[smp_processor_id()];
> >  	void **input_arg;
> > -	struct page *pg;
> > +	struct page *input_pg;
> >  
> >  	input_arg = (void **)this_cpu_ptr(hyperv_pcpu_input_arg);
> >  	/* hv_cpu_init() can be called with IRQs disabled from hv_resume() */
> > -	pg = alloc_page(irqs_disabled() ? GFP_ATOMIC : GFP_KERNEL);
> > -	if (unlikely(!pg))
> > +	input_pg = alloc_page(irqs_disabled() ? GFP_ATOMIC : GFP_KERNEL);
> > +	if (unlikely(!input_pg))
> >  		return -ENOMEM;
> > -	*input_arg = page_address(pg);
> > +	*input_arg = page_address(input_pg);
> > +
> > +	if (hv_root_partition) {
> > +		struct page *output_pg;
> > +		void **output_arg;
> > +
> > +		output_pg = alloc_page(irqs_disabled() ? GFP_ATOMIC :
> >  	GFP_KERNEL);
> 
> To simplify the code, can we just rename 'input_arg' to 'hypercall_args'
> and do alloc_pages(rqs_disabled() ? GFP_ATOMIC : GFP_KERNEL, 1) to
> allocate two pages above?

It should be doable, but I need to code it up and test it to be 100%
sure.

> 
> >  
[...]
> > +	/* Allocate the per-CPU state for output arg for root */
> > +	if (hv_root_partition) {
> > +		hyperv_pcpu_output_arg = alloc_percpu(void  *);
> 					redundant space ^^^^^

Fixed. Thanks. This is in fact copied from the input_arg code, so there
is a similar issue there to be fixed. But that's going to wait till
another day.

Wei.