[PATCH kvmtool] x86: Fixed Unable to execute init process since glibc version 2.33

[PATCH kvmtool] x86: Fixed Unable to execute init process since glibc version 2.33

[Dongli Si]

From: Dongli Si <sidongli1997@gmail.com>

glibc detected invalid CPU Vendor name will cause an error:

[    0.450127] Run /sbin/init as init process
/lib64/libc.so.6: CPU ISA level is lower than required
[    0.451931] Kernel panic - not syncing: Attempted to kill init! exitcode=0x00007f00
[    0.452117] CPU: 0 PID: 1 Comm: init Not tainted 5.17.0-rc1 #72

Signed-off-by: Dongli Si <sidongli1997@gmail.com>
---
 x86/cpuid.c | 14 +++++++++-----
 1 file changed, 9 insertions(+), 5 deletions(-)

diff --git a/x86/cpuid.c b/x86/cpuid.c
index c3b67d9..d58a027 100644
--- a/x86/cpuid.c
+++ b/x86/cpuid.c
@@ -2,6 +2,7 @@
 
 #include "kvm/kvm.h"
 #include "kvm/util.h"
+#include "kvm/cpufeature.h"
 
 #include <sys/ioctl.h>
 #include <stdlib.h>
@@ -10,7 +11,7 @@
 
 static void filter_cpuid(struct kvm_cpuid2 *kvm_cpuid)
 {
-	unsigned int signature[3];
+	struct cpuid_regs regs;
 	unsigned int i;
 
 	/*
@@ -22,10 +23,13 @@ static void filter_cpuid(struct kvm_cpuid2 *kvm_cpuid)
 		switch (entry->function) {
 		case 0:
 			/* Vendor name */
-			memcpy(signature, "LKVMLKVMLKVM", 12);
-			entry->ebx = signature[0];
-			entry->ecx = signature[1];
-			entry->edx = signature[2];
+			regs = (struct cpuid_regs) {
+				.eax		= 0x00,
+			};
+			host_cpuid(&regs);
+			entry->ebx = regs.ebx;
+			entry->ecx = regs.ecx;
+			entry->edx = regs.edx;
 			break;
 		case 1:
 			/* Set X86_FEATURE_HYPERVISOR */
-- 
2.32.0

Re: [PATCH kvmtool] x86: Fixed Unable to execute init process since glibc version 2.33

[Alexandru Elisei]

Hi,

On Sat, Feb 26, 2022 at 02:00:48PM +0800, Dongli Si wrote:
> From: Dongli Si <sidongli1997@gmail.com>
> 
> glibc detected invalid CPU Vendor name will cause an error:
> 
> [    0.450127] Run /sbin/init as init process
> /lib64/libc.so.6: CPU ISA level is lower than required
> [    0.451931] Kernel panic - not syncing: Attempted to kill init! exitcode=0x00007f00
> [    0.452117] CPU: 0 PID: 1 Comm: init Not tainted 5.17.0-rc1 #72

This looks bad. I'll try to reproduce it and I'll give my Tested-by tag after I
test it.

Thanks,
Alex

> 
> Signed-off-by: Dongli Si <sidongli1997@gmail.com>
> ---
>  x86/cpuid.c | 14 +++++++++-----
>  1 file changed, 9 insertions(+), 5 deletions(-)
> 
> diff --git a/x86/cpuid.c b/x86/cpuid.c
> index c3b67d9..d58a027 100644
> --- a/x86/cpuid.c
> +++ b/x86/cpuid.c
> @@ -2,6 +2,7 @@
>  
>  #include "kvm/kvm.h"
>  #include "kvm/util.h"
> +#include "kvm/cpufeature.h"
>  
>  #include <sys/ioctl.h>
>  #include <stdlib.h>
> @@ -10,7 +11,7 @@
>  
>  static void filter_cpuid(struct kvm_cpuid2 *kvm_cpuid)
>  {
> -	unsigned int signature[3];
> +	struct cpuid_regs regs;
>  	unsigned int i;
>  
>  	/*
> @@ -22,10 +23,13 @@ static void filter_cpuid(struct kvm_cpuid2 *kvm_cpuid)
>  		switch (entry->function) {
>  		case 0:
>  			/* Vendor name */
> -			memcpy(signature, "LKVMLKVMLKVM", 12);
> -			entry->ebx = signature[0];
> -			entry->ecx = signature[1];
> -			entry->edx = signature[2];
> +			regs = (struct cpuid_regs) {
> +				.eax		= 0x00,
> +			};
> +			host_cpuid(&regs);
> +			entry->ebx = regs.ebx;
> +			entry->ecx = regs.ecx;
> +			entry->edx = regs.edx;
>  			break;
>  		case 1:
>  			/* Set X86_FEATURE_HYPERVISOR */
> -- 
> 2.32.0
> 

Re: [PATCH kvmtool] x86: Fixed Unable to execute init process since glibc version 2.33

[Alexandru Elisei]

Hi,

Hi, I was unable to apply the patch as is because your base is missing
commit 20b93be583f6 ("x86: Set the correct APIC ID"). Changing it is so it
applies was trivial though.

I tested the patch with a VM image using glibc 2.36 and Linux v5.17-rc7,
the glibc error went away and I was able to boot to userspace; as an added
bonus, this kernel message went away:

[    0.000000] CPU: vendor_id 'LKVMLKVMLKVM' unknown, using generic init.
[    0.000000] CPU: Your system may be unstable.

But this warning is new:

[    0.000000] [Firmware Bug]: TSC doesn't count with P0 frequency!

I don't know what causes it (kvmtool's bios implementation is not feature
complete with regards to my CPU features?), and doesn't look like it's
something introduced by this patch, so as far as I'm concerned the patch is
working as intended:

Tested-by: Alexandru Elisei <alexandru.elisei@arm.com>

Thanks,
Alex

On Sat, Feb 26, 2022 at 02:00:48PM +0800, Dongli Si wrote:
> From: Dongli Si <sidongli1997@gmail.com>
> 
> glibc detected invalid CPU Vendor name will cause an error:
> 
> [    0.450127] Run /sbin/init as init process
> /lib64/libc.so.6: CPU ISA level is lower than required
> [    0.451931] Kernel panic - not syncing: Attempted to kill init! exitcode=0x00007f00
> [    0.452117] CPU: 0 PID: 1 Comm: init Not tainted 5.17.0-rc1 #72
> 
> Signed-off-by: Dongli Si <sidongli1997@gmail.com>
> ---
>  x86/cpuid.c | 14 +++++++++-----
>  1 file changed, 9 insertions(+), 5 deletions(-)
> 
> diff --git a/x86/cpuid.c b/x86/cpuid.c
> index c3b67d9..d58a027 100644
> --- a/x86/cpuid.c
> +++ b/x86/cpuid.c
> @@ -2,6 +2,7 @@
>  
>  #include "kvm/kvm.h"
>  #include "kvm/util.h"
> +#include "kvm/cpufeature.h"
>  
>  #include <sys/ioctl.h>
>  #include <stdlib.h>
> @@ -10,7 +11,7 @@
>  
>  static void filter_cpuid(struct kvm_cpuid2 *kvm_cpuid)
>  {
> -	unsigned int signature[3];
> +	struct cpuid_regs regs;
>  	unsigned int i;
>  
>  	/*
> @@ -22,10 +23,13 @@ static void filter_cpuid(struct kvm_cpuid2 *kvm_cpuid)
>  		switch (entry->function) {
>  		case 0:
>  			/* Vendor name */
> -			memcpy(signature, "LKVMLKVMLKVM", 12);
> -			entry->ebx = signature[0];
> -			entry->ecx = signature[1];
> -			entry->edx = signature[2];
> +			regs = (struct cpuid_regs) {
> +				.eax		= 0x00,
> +			};
> +			host_cpuid(&regs);
> +			entry->ebx = regs.ebx;
> +			entry->ecx = regs.ecx;
> +			entry->edx = regs.edx;
>  			break;
>  		case 1:
>  			/* Set X86_FEATURE_HYPERVISOR */
> -- 
> 2.32.0
> 

Re: [PATCH kvmtool] x86: Fixed Unable to execute init process since glibc version 2.33

[Andre Przywara]

On Sat, 26 Feb 2022 14:00:48 +0800
Dongli Si <sidongli1997@gmail.com> wrote:

Hi,

> From: Dongli Si <sidongli1997@gmail.com>
> 
> glibc detected invalid CPU Vendor name will cause an error:
> 
> [    0.450127] Run /sbin/init as init process
> /lib64/libc.so.6: CPU ISA level is lower than required
> [    0.451931] Kernel panic - not syncing: Attempted to kill init! exitcode=0x00007f00
> [    0.452117] CPU: 0 PID: 1 Comm: init Not tainted 5.17.0-rc1 #72
> 
> Signed-off-by: Dongli Si <sidongli1997@gmail.com>
> ---
>  x86/cpuid.c | 14 +++++++++-----
>  1 file changed, 9 insertions(+), 5 deletions(-)
> 
> diff --git a/x86/cpuid.c b/x86/cpuid.c
> index c3b67d9..d58a027 100644
> --- a/x86/cpuid.c
> +++ b/x86/cpuid.c
> @@ -2,6 +2,7 @@
>  
>  #include "kvm/kvm.h"
>  #include "kvm/util.h"
> +#include "kvm/cpufeature.h"
>  
>  #include <sys/ioctl.h>
>  #include <stdlib.h>
> @@ -10,7 +11,7 @@
>  
>  static void filter_cpuid(struct kvm_cpuid2 *kvm_cpuid)
>  {
> -	unsigned int signature[3];
> +	struct cpuid_regs regs;
>  	unsigned int i;
>  
>  	/*
> @@ -22,10 +23,13 @@ static void filter_cpuid(struct kvm_cpuid2 *kvm_cpuid)
>  		switch (entry->function) {
>  		case 0:
>  			/* Vendor name */
> -			memcpy(signature, "LKVMLKVMLKVM", 12);
> -			entry->ebx = signature[0];
> -			entry->ecx = signature[1];
> -			entry->edx = signature[2];
> +			regs = (struct cpuid_regs) {
> +				.eax		= 0x00,
> +			};
> +			host_cpuid(&regs);
> +			entry->ebx = regs.ebx;
> +			entry->ecx = regs.ecx;
> +			entry->edx = regs.edx;

But that's redundant, isn't it? We already get the host vendor ID in the
three registers in entry, and the current code is just there to overwrite
this. So just removing the whole "case 0:" part should do the trick.

Also please be aware that there was a reason for this fixup, as explained
in commit bc0b99a2a740 ("kvm tools: Filter out CPU vendor string").

Alex, did you boot this on an AMD box, to spot if this is still an issue?

Cheers,
Andre



>  			break;
>  		case 1:
>  			/* Set X86_FEATURE_HYPERVISOR */

Re: [PATCH kvmtool] x86: Fixed Unable to execute init process since glibc version 2.33

[Alexandru Elisei]

Hi,

On Tue, Mar 08, 2022 at 05:31:25PM +0000, Andre Przywara wrote:
> On Sat, 26 Feb 2022 14:00:48 +0800
> Dongli Si <sidongli1997@gmail.com> wrote:
> 
> Hi,
> 
> > From: Dongli Si <sidongli1997@gmail.com>
> > 
> > glibc detected invalid CPU Vendor name will cause an error:
> > 
> > [    0.450127] Run /sbin/init as init process
> > /lib64/libc.so.6: CPU ISA level is lower than required
> > [    0.451931] Kernel panic - not syncing: Attempted to kill init! exitcode=0x00007f00
> > [    0.452117] CPU: 0 PID: 1 Comm: init Not tainted 5.17.0-rc1 #72
> > 
> > Signed-off-by: Dongli Si <sidongli1997@gmail.com>
> > ---
> >  x86/cpuid.c | 14 +++++++++-----
> >  1 file changed, 9 insertions(+), 5 deletions(-)
> > 
> > diff --git a/x86/cpuid.c b/x86/cpuid.c
> > index c3b67d9..d58a027 100644
> > --- a/x86/cpuid.c
> > +++ b/x86/cpuid.c
> > @@ -2,6 +2,7 @@
> >  
> >  #include "kvm/kvm.h"
> >  #include "kvm/util.h"
> > +#include "kvm/cpufeature.h"
> >  
> >  #include <sys/ioctl.h>
> >  #include <stdlib.h>
> > @@ -10,7 +11,7 @@
> >  
> >  static void filter_cpuid(struct kvm_cpuid2 *kvm_cpuid)
> >  {
> > -	unsigned int signature[3];
> > +	struct cpuid_regs regs;
> >  	unsigned int i;
> >  
> >  	/*
> > @@ -22,10 +23,13 @@ static void filter_cpuid(struct kvm_cpuid2 *kvm_cpuid)
> >  		switch (entry->function) {
> >  		case 0:
> >  			/* Vendor name */
> > -			memcpy(signature, "LKVMLKVMLKVM", 12);
> > -			entry->ebx = signature[0];
> > -			entry->ecx = signature[1];
> > -			entry->edx = signature[2];
> > +			regs = (struct cpuid_regs) {
> > +				.eax		= 0x00,
> > +			};
> > +			host_cpuid(&regs);
> > +			entry->ebx = regs.ebx;
> > +			entry->ecx = regs.ecx;
> > +			entry->edx = regs.edx;
> 
> But that's redundant, isn't it? We already get the host vendor ID in the
> three registers in entry, and the current code is just there to overwrite
> this. So just removing the whole "case 0:" part should do the trick.
> 
> Also please be aware that there was a reason for this fixup, as explained
> in commit bc0b99a2a740 ("kvm tools: Filter out CPU vendor string").
> 
> Alex, did you boot this on an AMD box, to spot if this is still an issue?

I did a boot on an AMD Ryzen 3900x, didn't find any issues. But I don't
think a sample of one CPU is representative, so I'm not sure if the error
will not manifest with other models which exist now, or be released in the
future.

From what I can tell, kvmtool doesn't use KVM_X86_SET_MSR_FILTER, and the
default behaviour for KVM is to try to emulate the accesses to the MSRs in
the kernel instead of reflecting them to userspace. So I guess if the user
is running kvmtool on a very new AMD or Intel CPU (one of the CPUs
mentioned in the commit message for the fix was an engineering sample, for
example) for which KVM doesn't have full support, the error can manifest
again.

I'm not sure adding code to emulate a specific CPU is the right solution
for kvmtool. So I'm thinking either use the host CPU and tolerate the KVM
error messages, the frequency of which depends on how fast new MSRs are
added to KVM (I have no clue about that), or choose a very simple CPU model
that can be emulated by a particular version of KVM.

Thoughts?

Thanks,
Alex

Re: [PATCH kvmtool] x86: Fixed Unable to execute init process since glibc version 2.33

[Andre Przywara]

On Tue, 8 Mar 2022 17:31:25 +0000
Andre Przywara <andre.przywara@arm.com> wrote:

Hi,

I did some digging on this issue, see below:

> On Sat, 26 Feb 2022 14:00:48 +0800
> Dongli Si <sidongli1997@gmail.com> wrote:
> 
> Hi,
> 
> > From: Dongli Si <sidongli1997@gmail.com>
> > 
> > glibc detected invalid CPU Vendor name will cause an error:
> > 
> > [    0.450127] Run /sbin/init as init process
> > /lib64/libc.so.6: CPU ISA level is lower than required
> > [    0.451931] Kernel panic - not syncing: Attempted to kill init!
> > exitcode=0x00007f00 [    0.452117] CPU: 0 PID: 1 Comm: init Not
> > tainted 5.17.0-rc1 #72
> > 
> > Signed-off-by: Dongli Si <sidongli1997@gmail.com>
> > ---
> >  x86/cpuid.c | 14 +++++++++-----
> >  1 file changed, 9 insertions(+), 5 deletions(-)
> > 
> > diff --git a/x86/cpuid.c b/x86/cpuid.c
> > index c3b67d9..d58a027 100644
> > --- a/x86/cpuid.c
> > +++ b/x86/cpuid.c
> > @@ -2,6 +2,7 @@
> >  
> >  #include "kvm/kvm.h"
> >  #include "kvm/util.h"
> > +#include "kvm/cpufeature.h"
> >  
> >  #include <sys/ioctl.h>
> >  #include <stdlib.h>
> > @@ -10,7 +11,7 @@
> >  
> >  static void filter_cpuid(struct kvm_cpuid2 *kvm_cpuid)
> >  {
> > -	unsigned int signature[3];
> > +	struct cpuid_regs regs;
> >  	unsigned int i;
> >  
> >  	/*
> > @@ -22,10 +23,13 @@ static void filter_cpuid(struct kvm_cpuid2
> > *kvm_cpuid) switch (entry->function) {
> >  		case 0:
> >  			/* Vendor name */
> > -			memcpy(signature, "LKVMLKVMLKVM", 12);
> > -			entry->ebx = signature[0];
> > -			entry->ecx = signature[1];
> > -			entry->edx = signature[2];
> > +			regs = (struct cpuid_regs) {
> > +				.eax		= 0x00,
> > +			};
> > +			host_cpuid(&regs);
> > +			entry->ebx = regs.ebx;
> > +			entry->ecx = regs.ecx;
> > +			entry->edx = regs.edx;  
> 
> But that's redundant, isn't it? We already get the host vendor ID in the
> three registers in entry, and the current code is just there to overwrite
> this. So just removing the whole "case 0:" part should do the trick.
> 
> Also please be aware that there was a reason for this fixup, as explained
> in commit bc0b99a2a740 ("kvm tools: Filter out CPU vendor string").
> 
So I had a closer look, this is some background:

1) x86 is in the process of stepping up the minimum requirements for the
ISA level, so older x86-64 CPUs might not be supported anymore by some
distros. As a part of this, glibc allows to set a minimum required CPU,
and has a runtime check to verify compatibility:
https://sourceware.org/git/?p=glibc.git;a=blob;f=sysdeps/x86/cpu-features.c;h=514226b37889;hb=HEAD#l398
This routine first checks the vendor string, and only does very basic
capability checks if an unknown vendor (not AMD/Centaur/Intel) is detected.
The AMD manual (APM Vol. 3, 24594 Rev 3.3), CPUID instruction, states:
===============
For AMD processors, the string is AuthenticAMD. This string informs
software that it should follow the AMD CPUID definition for subsequent
CPUID function calls. If the function returns another vendor’s string,
software must use that vendor’s CPUID definition when interpreting
the results of subsequent CPUID function calls.
===============

So kvmtool using "LKVMLKVMLKVM" as the vendor string will probably end up
as detecting only the minimum CPU ISA level, which means glibc's built to
a higher standard will fail, as reported.
On top of that glibc problem the kernel also does various CPU checks, and
will deny features if an unknown vendor is detected. There are already
warnings in the kernel boot log today because of this.

2) The above mentioned kvmtool commit bc0b99a2a740 switched away from
keeping the host's vendor ID, because certain errata workarounds triggered
when the guest saw the host CPU vendor/family/model/stepping values. This
led to random MSR accesses, which KVM could not deal well with at the
time. KVM has improved since, and has code to deal with #GP injections due
to not-emulated MSR accesses. The particular first issue mentioned in the
above commit for instance is addressed by Linux commit d47cc0db8fd6:
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=d47cc0db8fd6

In general I remember that using random vendor strings was dismissed as a
good idea years ago, and other VMMs and hypervisors tend to inject either
the host's vendor string or at least a well-known value. So any Linux
guest issues due to certain vendor strings would apply to other VMMs or
HVs as well, and are probably fixed already.


So the problem with glibc is out there, and is there to stay. The
algorithm of checking for the vendor string first is correct by the books,
although arguably technically not strictly needed. But we cannot fix this,
so have to deal with it.

> Alex, did you boot this on an AMD box, to spot if this is still an issue?

I gave it a try on an old AMD box similar to the one in mentioned in the
commit message, and it worked fine with the native vendor string.

So I would suggest to just revert kvmtool commit bc0b99a2a740. I will send
a patch to that effect, unless someone objects now.


Cheers,
Andre

Re: [PATCH kvmtool] x86: Fixed Unable to execute init process since glibc version 2.33

[Alexandru Elisei]

Hi,

On Fri, Mar 11, 2022 at 12:10:42PM +0000, Andre Przywara wrote:
> On Tue, 8 Mar 2022 17:31:25 +0000
> Andre Przywara <andre.przywara@arm.com> wrote:
> 
> Hi,
> 
> I did some digging on this issue, see below:
> 
> > On Sat, 26 Feb 2022 14:00:48 +0800
> > Dongli Si <sidongli1997@gmail.com> wrote:
> > 
> > Hi,
> > 
> > > From: Dongli Si <sidongli1997@gmail.com>
> > > 
> > > glibc detected invalid CPU Vendor name will cause an error:
> > > 
> > > [    0.450127] Run /sbin/init as init process
> > > /lib64/libc.so.6: CPU ISA level is lower than required
> > > [    0.451931] Kernel panic - not syncing: Attempted to kill init!
> > > exitcode=0x00007f00 [    0.452117] CPU: 0 PID: 1 Comm: init Not
> > > tainted 5.17.0-rc1 #72
> > > 
> > > Signed-off-by: Dongli Si <sidongli1997@gmail.com>
> > > ---
> > >  x86/cpuid.c | 14 +++++++++-----
> > >  1 file changed, 9 insertions(+), 5 deletions(-)
> > > 
> > > diff --git a/x86/cpuid.c b/x86/cpuid.c
> > > index c3b67d9..d58a027 100644
> > > --- a/x86/cpuid.c
> > > +++ b/x86/cpuid.c
> > > @@ -2,6 +2,7 @@
> > >  
> > >  #include "kvm/kvm.h"
> > >  #include "kvm/util.h"
> > > +#include "kvm/cpufeature.h"
> > >  
> > >  #include <sys/ioctl.h>
> > >  #include <stdlib.h>
> > > @@ -10,7 +11,7 @@
> > >  
> > >  static void filter_cpuid(struct kvm_cpuid2 *kvm_cpuid)
> > >  {
> > > -	unsigned int signature[3];
> > > +	struct cpuid_regs regs;
> > >  	unsigned int i;
> > >  
> > >  	/*
> > > @@ -22,10 +23,13 @@ static void filter_cpuid(struct kvm_cpuid2
> > > *kvm_cpuid) switch (entry->function) {
> > >  		case 0:
> > >  			/* Vendor name */
> > > -			memcpy(signature, "LKVMLKVMLKVM", 12);
> > > -			entry->ebx = signature[0];
> > > -			entry->ecx = signature[1];
> > > -			entry->edx = signature[2];
> > > +			regs = (struct cpuid_regs) {
> > > +				.eax		= 0x00,
> > > +			};
> > > +			host_cpuid(&regs);
> > > +			entry->ebx = regs.ebx;
> > > +			entry->ecx = regs.ecx;
> > > +			entry->edx = regs.edx;  
> > 
> > But that's redundant, isn't it? We already get the host vendor ID in the
> > three registers in entry, and the current code is just there to overwrite
> > this. So just removing the whole "case 0:" part should do the trick.
> > 
> > Also please be aware that there was a reason for this fixup, as explained
> > in commit bc0b99a2a740 ("kvm tools: Filter out CPU vendor string").
> > 
> So I had a closer look, this is some background:
> 
> 1) x86 is in the process of stepping up the minimum requirements for the
> ISA level, so older x86-64 CPUs might not be supported anymore by some
> distros. As a part of this, glibc allows to set a minimum required CPU,
> and has a runtime check to verify compatibility:
> https://sourceware.org/git/?p=glibc.git;a=blob;f=sysdeps/x86/cpu-features.c;h=514226b37889;hb=HEAD#l398
> This routine first checks the vendor string, and only does very basic
> capability checks if an unknown vendor (not AMD/Centaur/Intel) is detected.
> The AMD manual (APM Vol. 3, 24594 Rev 3.3), CPUID instruction, states:
> ===============
> For AMD processors, the string is AuthenticAMD. This string informs
> software that it should follow the AMD CPUID definition for subsequent
> CPUID function calls. If the function returns another vendor’s string,
> software must use that vendor’s CPUID definition when interpreting
> the results of subsequent CPUID function calls.
> ===============
> 
> So kvmtool using "LKVMLKVMLKVM" as the vendor string will probably end up
> as detecting only the minimum CPU ISA level, which means glibc's built to
> a higher standard will fail, as reported.
> On top of that glibc problem the kernel also does various CPU checks, and
> will deny features if an unknown vendor is detected. There are already
> warnings in the kernel boot log today because of this.
> 
> 2) The above mentioned kvmtool commit bc0b99a2a740 switched away from
> keeping the host's vendor ID, because certain errata workarounds triggered
> when the guest saw the host CPU vendor/family/model/stepping values. This
> led to random MSR accesses, which KVM could not deal well with at the
> time. KVM has improved since, and has code to deal with #GP injections due
> to not-emulated MSR accesses. The particular first issue mentioned in the
> above commit for instance is addressed by Linux commit d47cc0db8fd6:
> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=d47cc0db8fd6
> 
> In general I remember that using random vendor strings was dismissed as a
> good idea years ago, and other VMMs and hypervisors tend to inject either
> the host's vendor string or at least a well-known value. So any Linux
> guest issues due to certain vendor strings would apply to other VMMs or
> HVs as well, and are probably fixed already.
> 
> 
> So the problem with glibc is out there, and is there to stay. The
> algorithm of checking for the vendor string first is correct by the books,
> although arguably technically not strictly needed. But we cannot fix this,
> so have to deal with it.
> 
> > Alex, did you boot this on an AMD box, to spot if this is still an issue?
> 
> I gave it a try on an old AMD box similar to the one in mentioned in the
> commit message, and it worked fine with the native vendor string.
> 
> So I would suggest to just revert kvmtool commit bc0b99a2a740. I will send
> a patch to that effect, unless someone objects now.

Thank you for the detailed explanation!

I too think that reverting the commit that added the custom vendor string
is the best way to fix the glibc errors in a guest.

Thanks,
Alex