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

From: Wei Liu <wei.liu@kernel.org>
To: Vitaly Kuznetsov <vkuznets@redhat.com>
Cc: Wei Liu <wei.liu@kernel.org>,
	Linux on Hyper-V List <linux-hyperv@vger.kernel.org>,
	virtualization@lists.linux-foundation.org,
	Linux Kernel List <linux-kernel@vger.kernel.org>,
	Michael Kelley <mikelley@microsoft.com>,
	Vineeth Pillai <viremana@linux.microsoft.com>,
	Sunil Muthuswamy <sunilmut@microsoft.com>,
	Nuno Das Neves <nudasnev@microsoft.com>,
	Lillian Grassin-Drake <ligrassi@microsoft.com>,
	"K. Y. Srinivasan" <kys@microsoft.com>,
	Haiyang Zhang <haiyangz@microsoft.com>,
	Stephen Hemminger <sthemmin@microsoft.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
	"maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)"
	<x86@kernel.org>, "H. Peter Anvin" <hpa@zytor.com>
Subject: Re: [PATCH RFC v1 06/18] x86/hyperv: allocate output arg pages if required
Date: Wed, 16 Sep 2020 15:42:00 +0000	[thread overview]
Message-ID: <20200916154200.7nf74vjmqu3f6sfq@liuwe-devbox-debian-v2> (raw)
In-Reply-To: <20200915124318.z6tisek5y4d7e254@liuwe-devbox-debian-v2>

On Tue, Sep 15, 2020 at 12:43:18PM +0000, Wei Liu wrote:
> On Tue, Sep 15, 2020 at 12:16:58PM +0200, Vitaly Kuznetsov wrote:
> > Wei Liu <wei.liu@kernel.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@microsoft.com>
> > > Co-Developed-by: Lillian Grassin-Drake <ligrassi@microsoft.com>
> > > Signed-off-by: Wei Liu <wei.liu@kernel.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.
> 

I switch to alloc_pages to allocate an order of 2 page if necessary, but
I keep input_arg and output_arg separate because I want to avoid code
churn in other places.

Wei.

> > 
> > >  
> [...]
> > > +	/* 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.