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

From: Vitaly Kuznetsov <vkuznets@redhat.com>
To: Wei Liu <wei.liu@kernel.org>,
	Linux on Hyper-V List <linux-hyperv@vger.kernel.org>
Cc: 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>,
	Wei Liu <wei.liu@kernel.org>,
	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: Tue, 15 Sep 2020 12:16:58 +0200	[thread overview]
Message-ID: <871rj3l4yt.fsf@vitty.brq.redhat.com> (raw)
In-Reply-To: <20200914112802.80611-7-wei.liu@kernel.org>

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?

> +		if (unlikely(!output_pg)) {
> +			free_page((unsigned long)*input_arg);
> +			*input_arg = NULL;
> +			return -ENOMEM;
> +		}
> +
> +		output_arg = (void **)this_cpu_ptr(hyperv_pcpu_output_arg);
> +		*output_arg = page_address(output_pg);
> +	}
>  
>  	hv_get_vp_index(msr_vp_index);
>  
> @@ -209,14 +227,25 @@ static int hv_cpu_die(unsigned int cpu)
>  	unsigned int new_cpu;
>  	unsigned long flags;
>  	void **input_arg;
> -	void *input_pg = NULL;
> +	void *input_pg = NULL, *output_pg = NULL;
>  
>  	local_irq_save(flags);
>  	input_arg = (void **)this_cpu_ptr(hyperv_pcpu_input_arg);
>  	input_pg = *input_arg;
>  	*input_arg = NULL;
> +
> +	if (hv_root_partition) {
> +		void **output_arg;
> +
> +		output_arg = (void **)this_cpu_ptr(hyperv_pcpu_output_arg);
> +		output_pg = *output_arg;
> +		*output_arg = NULL;
> +	}
> +
>  	local_irq_restore(flags);
> +
>  	free_page((unsigned long)input_pg);
> +	free_page((unsigned long)output_pg);
>  
>  	if (hv_vp_assist_page && hv_vp_assist_page[cpu])
>  		wrmsrl(HV_X64_MSR_VP_ASSIST_PAGE, 0);
> @@ -350,6 +379,12 @@ void __init hyperv_init(void)
>  
>  	BUG_ON(hyperv_pcpu_input_arg == NULL);
>  
> +	/* Allocate the per-CPU state for output arg for root */
> +	if (hv_root_partition) {
> +		hyperv_pcpu_output_arg = alloc_percpu(void  *);
					redundant space ^^^^^

> +		BUG_ON(hyperv_pcpu_output_arg == NULL);
> +	}
> +
>  	/* Allocate percpu VP index */
>  	hv_vp_index = kmalloc_array(num_possible_cpus(), sizeof(*hv_vp_index),
>  				    GFP_KERNEL);
> diff --git a/arch/x86/include/asm/mshyperv.h b/arch/x86/include/asm/mshyperv.h
> index 2a2cc81beac6..f5c62140f28d 100644
> --- a/arch/x86/include/asm/mshyperv.h
> +++ b/arch/x86/include/asm/mshyperv.h
> @@ -63,6 +63,7 @@ static inline void hv_disable_stimer0_percpu_irq(int irq) {}
>  #if IS_ENABLED(CONFIG_HYPERV)
>  extern void *hv_hypercall_pg;
>  extern void  __percpu  **hyperv_pcpu_input_arg;
> +extern void  __percpu  **hyperv_pcpu_output_arg;
>  
>  static inline u64 hv_do_hypercall(u64 control, void *input, void *output)
>  {

-- 
Vitaly