RE: [RFC Patch 1/3] X86/Hyper-V: Add flush HvFlushGuestPhysicalAddressSpace hypercall support

[Michael Kelley (EOSG)]

> -----Original Message-----
> From: linux-kernel-owner@xxxxxxxxxxxxxxx <linux-kernel-owner@xxxxxxxxxxxxxxx> On Behalf
> Of Tianyu Lan
> Sent: Monday, June 4, 2018 2:08 AM
> Cc: Tianyu Lan <Tianyu.Lan@xxxxxxxxxxxxx>; KY Srinivasan <kys@xxxxxxxxxxxxx>; Haiyang
> Zhang <haiyangz@xxxxxxxxxxxxx>; Stephen Hemminger <sthemmin@xxxxxxxxxxxxx>;
> tglx@xxxxxxxxxxxxx; mingo@xxxxxxxxxx; hpa@xxxxxxxxx; x86@xxxxxxxxxx;
> pbonzini@xxxxxxxxxx; rkrcmar@xxxxxxxxxx; devel@xxxxxxxxxxxxxxxxxxxxxx; linux-
> kernel@xxxxxxxxxxxxxxx; kvm@xxxxxxxxxxxxxxx; vkuznets@xxxxxxxxxx
> Subject: [RFC Patch 1/3] X86/Hyper-V: Add flush HvFlushGuestPhysicalAddressSpace hypercall
> support
> 
> Hyper-V provides a pv hypercall HvFlushGuestPhysicalAddressSpace to flush
> nested VM address space mapping in l1 hypervisor and it's to reduce overhead
> of flushing ept tlb among vcpus. This patch is to implement it.
> 
> Signed-off-by: Lan Tianyu <Tianyu.Lan@xxxxxxxxxxxxx>
> ---
> diff --git a/arch/x86/hyperv/nested.c b/arch/x86/hyperv/nested.c
> new file mode 100644
> index 000000000000..17f7c288eccc
> --- /dev/null
> +++ b/arch/x86/hyperv/nested.c
> +#include <linux/types.h>
> +#include <asm/hyperv-tlfs.h>
> +#include <asm/mshyperv.h>
> +#include <asm/tlbflush.h>
> +
> +int hyperv_flush_guest_mapping(u64 as)
> +{
> +	struct hv_guest_mapping_flush **flush_pcpu;
> +	struct hv_guest_mapping_flush *flush;
> +	u64 status = U64_MAX;

Initializing status to U64_MAX doesn't seem necessary.

> +	unsigned long flags;
> +	int ret = -EFAULT;
> +
> +	if (!hv_hypercall_pg)
> +		goto fault;
> +
> +	local_irq_save(flags);
> +
> +	flush_pcpu = (struct hv_guest_mapping_flush **)
> +		this_cpu_ptr(hyperv_pcpu_input_arg);
> +
> +	flush = *flush_pcpu;
> +
> +	if (unlikely(!flush)) {
> +		local_irq_restore(flags);
> +		goto fault;
> +	}
> +
> +	flush->address_space = as;
> +	flush->flags = 0;
> +
> +	status = hv_do_hypercall(HVCALL_FLUSH_GUEST_PHYSICAL_ADDRESS_SPACE,
> +				 flush, NULL);
> +	local_irq_restore(flags);
> +
> +	if (!(status & HV_HYPERCALL_RESULT_MASK))
> +		ret = 0;
> +
> +fault:
> +	return ret;
> +}
> +EXPORT_SYMBOL_GPL(hyperv_flush_guest_mapping);
> diff --git a/arch/x86/include/asm/hyperv-tlfs.h b/arch/x86/include/asm/hyperv-tlfs.h
> index b8c89265baf0..53bbeb08faea 100644
> --- a/arch/x86/include/asm/hyperv-tlfs.h
> +++ b/arch/x86/include/asm/hyperv-tlfs.h
> @@ -309,6 +309,7 @@ struct ms_hyperv_tsc_page {
>  #define HV_X64_MSR_REENLIGHTENMENT_CONTROL	0x40000106
> 
>  /* Nested features (CPUID 0x4000000A) EAX */
> +#define HV_X64_NESTED_GUSET_MAPPING_FLUSH	BIT(18)

The #define name is misspelled.  "_GUSET_" should be "_GUEST_".
And the matching usage in patch 3/3 will need to be updated as well.

Michael