RE: [PATCH v5 08/16] x86/hyperv: handling hypercall page setup for root

[Michael Kelley via Virtualization <virtualization@lists.linux-foundation.org>]

From: Wei Liu <wei.liu@kernel.org> Sent: Wednesday, January 20, 2021 4:01 AM
> 
> When Linux is running as the root partition, the hypercall page will
> have already been setup by Hyper-V. Copy the content over to the
> allocated page.
> 
> Add checks to hv_suspend & co to bail early because they are not
> supported in this setup yet.
> 
> Signed-off-by: Lillian Grassin-Drake <ligrassi@microsoft.com>
> Signed-off-by: Sunil Muthuswamy <sunilmut@microsoft.com>
> Signed-off-by: Nuno Das Neves <nunodasneves@linux.microsoft.com>
> Co-Developed-by: Lillian Grassin-Drake <ligrassi@microsoft.com>
> Co-Developed-by: Sunil Muthuswamy <sunilmut@microsoft.com>
> Co-Developed-by: Nuno Das Neves <nunodasneves@linux.microsoft.com>
> Signed-off-by: Wei Liu <wei.liu@kernel.org>
> ---
> v3:
> 1. Use HV_HYP_PAGE_SIZE.
> 2. Add checks to hv_suspend & co.
> ---
>  arch/x86/hyperv/hv_init.c | 37 ++++++++++++++++++++++++++++++++++---
>  1 file changed, 34 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/x86/hyperv/hv_init.c b/arch/x86/hyperv/hv_init.c
> index fc9941bd8653..ad8e77859b32 100644
> --- a/arch/x86/hyperv/hv_init.c
> +++ b/arch/x86/hyperv/hv_init.c
> @@ -25,6 +25,7 @@
>  #include <linux/cpuhotplug.h>
>  #include <linux/syscore_ops.h>
>  #include <clocksource/hyperv_timer.h>
> +#include <linux/highmem.h>
> 
>  u64 hv_current_partition_id = ~0ull;
>  EXPORT_SYMBOL_GPL(hv_current_partition_id);
> @@ -283,6 +284,9 @@ static int hv_suspend(void)
>  	union hv_x64_msr_hypercall_contents hypercall_msr;
>  	int ret;
> 
> +	if (hv_root_partition)
> +		return -EPERM;
> +
>  	/*
>  	 * Reset the hypercall page as it is going to be invalidated
>  	 * accross hibernation. Setting hv_hypercall_pg to NULL ensures
> @@ -433,8 +437,35 @@ void __init hyperv_init(void)
> 
>  	rdmsrl(HV_X64_MSR_HYPERCALL, hypercall_msr.as_uint64);
>  	hypercall_msr.enable = 1;
> -	hypercall_msr.guest_physical_address = vmalloc_to_pfn(hv_hypercall_pg);
> -	wrmsrl(HV_X64_MSR_HYPERCALL, hypercall_msr.as_uint64);
> +
> +	if (hv_root_partition) {
> +		struct page *pg;
> +		void *src, *dst;
> +
> +		/*
> +		 * For the root partition, the hypervisor will set up its
> +		 * hypercall page. The hypervisor guarantees it will not show
> +		 * up in the root's address space. The root can't change the
> +		 * location of the hypercall page.
> +		 *
> +		 * Order is important here. We must enable the hypercall page
> +		 * so it is populated with code, then copy the code to an
> +		 * executable page.
> +		 */
> +		wrmsrl(HV_X64_MSR_HYPERCALL, hypercall_msr.as_uint64);
> +
> +		pg = vmalloc_to_page(hv_hypercall_pg);
> +		dst = kmap(pg);
> +		src = memremap(hypercall_msr.guest_physical_address << PAGE_SHIFT,
> PAGE_SIZE,
> +				MEMREMAP_WB);
> +		BUG_ON(!(src && dst));
> +		memcpy(dst, src, HV_HYP_PAGE_SIZE);
> +		memunmap(src);
> +		kunmap(pg);
> +	} else {
> +		hypercall_msr.guest_physical_address = vmalloc_to_pfn(hv_hypercall_pg);
> +		wrmsrl(HV_X64_MSR_HYPERCALL, hypercall_msr.as_uint64);
> +	}
> 
>  	/*
>  	 * Ignore any errors in setting up stimer clockevents
> @@ -577,6 +608,6 @@ EXPORT_SYMBOL_GPL(hv_is_hyperv_initialized);
> 
>  bool hv_is_hibernation_supported(void)
>  {
> -	return acpi_sleep_state_supported(ACPI_STATE_S4);
> +	return !hv_root_partition && acpi_sleep_state_supported(ACPI_STATE_S4);
>  }
>  EXPORT_SYMBOL_GPL(hv_is_hibernation_supported);
> --
> 2.20.1

Reviewed-by: Michael Kelley <mikelley@microsoft.com>

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