* [PATCH v2] x86/hyperv: Allow 15-bit APIC IDs for VTL platforms
@ 2024-01-15 17:57 Saurabh Sengar
2024-01-16 15:25 ` Michael Kelley
0 siblings, 1 reply; 3+ messages in thread
From: Saurabh Sengar @ 2024-01-15 17:57 UTC (permalink / raw)
To: kys, haiyangz, wei.liu, decui, tglx, mingo, bp, dave.hansen, x86,
hpa, linux-hyperv, linux-kernel
Cc: ssengar
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@linux.microsoft.com>
---
[V2]
- Modify commit message
arch/x86/hyperv/hv_vtl.c | 7 +++++++
1 file changed, 7 insertions(+)
diff --git a/arch/x86/hyperv/hv_vtl.c b/arch/x86/hyperv/hv_vtl.c
index 96e6c51..cf1b78c 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)
--
1.8.3.1
^ permalink raw reply related [flat|nested] 3+ messages in thread
* RE: [PATCH v2] x86/hyperv: Allow 15-bit APIC IDs for VTL platforms
2024-01-15 17:57 [PATCH v2] x86/hyperv: Allow 15-bit APIC IDs for VTL platforms Saurabh Sengar
@ 2024-01-16 15:25 ` Michael Kelley
2024-03-01 9:26 ` Wei Liu
0 siblings, 1 reply; 3+ messages in thread
From: Michael Kelley @ 2024-01-16 15:25 UTC (permalink / raw)
To: Saurabh Sengar, kys@microsoft.com, haiyangz@microsoft.com,
wei.liu@kernel.org, decui@microsoft.com, tglx@linutronix.de,
mingo@redhat.com, bp@alien8.de, dave.hansen@linux.intel.com,
x86@kernel.org, hpa@zytor.com, linux-hyperv@vger.kernel.org,
linux-kernel@vger.kernel.org
Cc: ssengar@microsoft.com
From: Saurabh Sengar <ssengar@linux.microsoft.com> Sent: Monday, January 15, 2024 9:58 AM
>
> 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@linux.microsoft.com>
> ---
> [V2]
> - Modify commit message
>
> arch/x86/hyperv/hv_vtl.c | 7 +++++++
> 1 file changed, 7 insertions(+)
>
> diff --git a/arch/x86/hyperv/hv_vtl.c b/arch/x86/hyperv/hv_vtl.c
> index 96e6c51..cf1b78c 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)
> --
> 1.8.3.1
>
Reviewed-by: Michael Kelley <mhklinux@outlook.com>
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [PATCH v2] x86/hyperv: Allow 15-bit APIC IDs for VTL platforms
2024-01-16 15:25 ` Michael Kelley
@ 2024-03-01 9:26 ` Wei Liu
0 siblings, 0 replies; 3+ messages in thread
From: Wei Liu @ 2024-03-01 9:26 UTC (permalink / raw)
To: Michael Kelley
Cc: Saurabh Sengar, kys@microsoft.com, haiyangz@microsoft.com,
wei.liu@kernel.org, decui@microsoft.com, tglx@linutronix.de,
mingo@redhat.com, bp@alien8.de, dave.hansen@linux.intel.com,
x86@kernel.org, hpa@zytor.com, linux-hyperv@vger.kernel.org,
linux-kernel@vger.kernel.org, ssengar@microsoft.com
On Tue, Jan 16, 2024 at 03:25:47PM +0000, Michael Kelley wrote:
> From: Saurabh Sengar <ssengar@linux.microsoft.com> Sent: Monday, January 15, 2024 9:58 AM
> >
> > 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@linux.microsoft.com>
[...]
>
> Reviewed-by: Michael Kelley <mhklinux@outlook.com>
Applied. Thanks.
^ permalink raw reply [flat|nested] 3+ messages in thread
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2024-01-15 17:57 [PATCH v2] x86/hyperv: Allow 15-bit APIC IDs for VTL platforms Saurabh Sengar
2024-01-16 15:25 ` Michael Kelley
2024-03-01 9:26 ` Wei Liu
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