Commit 0d63e4c0 authored by Saurabh Sengar's avatar Saurabh Sengar Committed by Wei Liu
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x86/hyperv: Allow 15-bit APIC IDs for VTL platforms 



The current method for signaling the compatibility of a Hyper-V host
with MSIs featuring 15-bit APIC IDs relies on a synthetic cpuid leaf.
However, for higher VTLs, this leaf is not reported, due to the absence
of an IO-APIC.

As an alternative, assume that when running at a high VTL, the host
supports 15-bit APIC IDs. This assumption is safe, as Hyper-V does not
employ any architectural MSIs at higher VTLs

This unblocks startup of VTL2 environments with more than 256 CPUs.

Signed-off-by: default avatarSaurabh Sengar <ssengar@linux.microsoft.com>
Reviewed-by: default avatarMichael Kelley <mhklinux@outlook.com>
Link: https://lore.kernel.org/r/1705341460-18394-1-git-send-email-ssengar@linux.microsoft.com


Signed-off-by: default avatarWei Liu <wei.liu@kernel.org>
Message-ID: <1705341460-18394-1-git-send-email-ssengar@linux.microsoft.com>
parent 0f34d112

arch/x86/hyperv/hv_vtl.c

+7 −0
Original line number Diff line number Diff line
@@ -16,6 +16,11 @@ 
extern struct boot_params boot_params;

static struct real_mode_header hv_vtl_real_mode_header;



static bool __init hv_vtl_msi_ext_dest_id(void)

{

	return true;

}



void __init hv_vtl_init_platform(void)

{

	pr_info("Linux runs in Hyper-V Virtual Trust Level\n");
@@ -38,6 +43,8 @@ void __init hv_vtl_init_platform(void) 
	x86_platform.legacy.warm_reset = 0;

	x86_platform.legacy.reserve_bios_regions = 0;

	x86_platform.legacy.devices.pnpbios = 0;



	x86_init.hyper.msi_ext_dest_id = hv_vtl_msi_ext_dest_id;

}



static inline u64 hv_vtl_system_desc_base(struct ldttss_desc *desc)