Patch "x86/hyperv: Allow 15-bit APIC IDs for VTL platforms" has been added to the 6.6-stable tree

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This is a note to let you know that I've just added the patch titled

    x86/hyperv: Allow 15-bit APIC IDs for VTL platforms

to the 6.6-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     x86-hyperv-allow-15-bit-apic-ids-for-vtl-platforms.patch
and it can be found in the queue-6.6 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit c97c49ed247f68435d5bb00a4d25373f818e00e6
Author: Saurabh Sengar <ssengar@xxxxxxxxxxxxxxxxxxx>
Date:   Mon Jan 15 09:57:40 2024 -0800

    x86/hyperv: Allow 15-bit APIC IDs for VTL platforms
    
    [ Upstream commit 0d63e4c0ebc2b5c329babde44fd61d3f08db814d ]
    
    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: Saurabh Sengar <ssengar@xxxxxxxxxxxxxxxxxxx>
    Reviewed-by: Michael Kelley <mhklinux@xxxxxxxxxxx>
    Link: https://lore.kernel.org/r/1705341460-18394-1-git-send-email-ssengar@xxxxxxxxxxxxxxxxxxx
    Signed-off-by: Wei Liu <wei.liu@xxxxxxxxxx>
    Message-ID: <1705341460-18394-1-git-send-email-ssengar@xxxxxxxxxxxxxxxxxxx>
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/arch/x86/hyperv/hv_vtl.c b/arch/x86/hyperv/hv_vtl.c
index 999f5ac82fe90..53b309d41b3b9 100644
--- a/arch/x86/hyperv/hv_vtl.c
+++ b/arch/x86/hyperv/hv_vtl.c
@@ -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)




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