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Date:   Wed, 2 Nov 2022 12:45:32 +0000
From:   Wei Liu <wei.liu@kernel.org>
To:     Stanislav Kinsburskii <skinsburskii@linux.microsoft.com>
Cc:     Stanislav Kinsburskiy <stanislav.kinsburskiy@gmail.com>,
        Andy Lutomirski <luto@kernel.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        Dave Hansen <dave.hansen@linux.intel.com>, x86@kernel.org,
        "H. Peter Anvin" <hpa@zytor.com>,
        "K. Y. Srinivasan" <kys@microsoft.com>,
        Haiyang Zhang <haiyangz@microsoft.com>,
        Wei Liu <wei.liu@kernel.org>, Dexuan Cui <decui@microsoft.com>,
        Daniel Lezcano <daniel.lezcano@linaro.org>,
        linux-kernel@vger.kernel.org, linux-hyperv@vger.kernel.org
Subject: Re: [PATCH 3/4] drivers/clocksource/hyper-v: Use TSC PFN getter to
 map vvar page
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On Tue, Nov 01, 2022 at 05:31:15PM +0000, Stanislav Kinsburskii wrote:
> From: Stanislav Kinsburskiy <stanislav.kinsburskiy@gmail.com>
> 
> Instead of converting the virtual address to physical directly.
> This is a precursor patch for the upcoming support for TSC page mapping into
> hyper-v root partition, which address will be defined by the hypervisor and

Please use "Microsoft Hypervisor" instead of "hyper-v".

Also, it should be "Hyper-V" not "hyper-v" in the future.

> mapped into the kernel.
> 
> Signed-off-by: Stanislav Kinsburskiy <stanislav.kinsburskiy@gmail.com>
> CC: Andy Lutomirski <luto@kernel.org>
> CC: Thomas Gleixner <tglx@linutronix.de>
> CC: Ingo Molnar <mingo@redhat.com>
> CC: Borislav Petkov <bp@alien8.de>
> CC: Dave Hansen <dave.hansen@linux.intel.com>
> CC: x86@kernel.org
> CC: "H. Peter Anvin" <hpa@zytor.com>
> CC: "K. Y. Srinivasan" <kys@microsoft.com>
> CC: Haiyang Zhang <haiyangz@microsoft.com>
> CC: Wei Liu <wei.liu@kernel.org>
> CC: Dexuan Cui <decui@microsoft.com>
> CC: Daniel Lezcano <daniel.lezcano@linaro.org>
> CC: linux-kernel@vger.kernel.org
> CC: linux-hyperv@vger.kernel.org
> ---
>  arch/x86/entry/vdso/vma.c          |    7 +++----
>  drivers/clocksource/hyperv_timer.c |    3 ++-
>  include/clocksource/hyperv_timer.h |    6 ++++++
>  3 files changed, 11 insertions(+), 5 deletions(-)
> 
> diff --git a/arch/x86/entry/vdso/vma.c b/arch/x86/entry/vdso/vma.c
> index 311eae30e089..6976416b2c9f 100644
> --- a/arch/x86/entry/vdso/vma.c
> +++ b/arch/x86/entry/vdso/vma.c
> @@ -210,11 +210,10 @@ static vm_fault_t vvar_fault(const struct vm_special_mapping *sm,
>  					pgprot_decrypted(vma->vm_page_prot));
>  		}
>  	} else if (sym_offset == image->sym_hvclock_page) {
> -		struct ms_hyperv_tsc_page *tsc_pg = hv_get_tsc_page();
> +		pfn = hv_get_tsc_pfn();
>  
> -		if (tsc_pg && vclock_was_used(VDSO_CLOCKMODE_HVCLOCK))
> -			return vmf_insert_pfn(vma, vmf->address,
> -					virt_to_phys(tsc_pg) >> PAGE_SHIFT);
> +		if (pfn && vclock_was_used(VDSO_CLOCKMODE_HVCLOCK))
> +			return vmf_insert_pfn(vma, vmf->address, pfn);

hv_get_tsc_pfn() can return 0. You will insert PFN 0 into the page
table. I think you should check if the PFN is valid.

>  	} else if (sym_offset == image->sym_timens_page) {
>  		struct page *timens_page = find_timens_vvar_page(vma);
>  
> diff --git a/drivers/clocksource/hyperv_timer.c b/drivers/clocksource/hyperv_timer.c
> index d447bc99a399..635c14c1e3bf 100644
> --- a/drivers/clocksource/hyperv_timer.c
> +++ b/drivers/clocksource/hyperv_timer.c
> @@ -369,10 +369,11 @@ static union {
>  static struct ms_hyperv_tsc_page *tsc_page = &tsc_pg.page;
>  static unsigned long tsc_pfn;
>  
> -static unsigned long hv_get_tsc_pfn(void)
> +unsigned long hv_get_tsc_pfn(void)
>  {
>  	return tsc_pfn;
>  }
> +EXPORT_SYMBOL_GPL(hv_get_tsc_pfn);
>  
>  struct ms_hyperv_tsc_page *hv_get_tsc_page(void)
>  {
> diff --git a/include/clocksource/hyperv_timer.h b/include/clocksource/hyperv_timer.h
> index b3f5d73ae1d6..3078d23faaea 100644
> --- a/include/clocksource/hyperv_timer.h
> +++ b/include/clocksource/hyperv_timer.h
> @@ -32,6 +32,7 @@ extern void hv_stimer0_isr(void);
>  
>  extern void hv_init_clocksource(void);
>  
> +extern unsigned long hv_get_tsc_pfn(void);
>  extern struct ms_hyperv_tsc_page *hv_get_tsc_page(void);
>  
>  static inline notrace u64
> @@ -90,6 +91,11 @@ hv_read_tsc_page(const struct ms_hyperv_tsc_page *tsc_pg)
>  }
>  
>  #else /* CONFIG_HYPERV_TIMER */
> +static inline unsigned long hv_get_tsc_pfn(void)
> +{
> +	return 0;
> +}
> +
>  static inline struct ms_hyperv_tsc_page *hv_get_tsc_page(void)
>  {
>  	return NULL;
> 
>