[PATCH] KVM: x86: Turn off KVM_WERROR by default for all configs

[PATCH] KVM: x86: Turn off KVM_WERROR by default for all configs

[Sean Christopherson]

Don't enable KVM_WERROR by default for x86-64 builds as KVM's one-off
-Werror enabling is *mostly* superseded by the kernel-wide WERROR, and
enabling KVM_WERROR by default can cause problems for developers working
on other subsystems.  E.g. subsystems that have a "zero W=1 regressions"
rule can inadvertently build KVM with -Werror and W=1, and end up with
build failures that are completely uninteresting to the developer (W=1 is
prone to false positives, especially on older compilers).

Keep KVM_WERROR as there are combinations where enabling WERROR isn't
feasible, e.g. the default FRAME_WARN=1024 on i386 builds generates a
non-zero number of warnings and thus errors, and there are far too many
warnings throughout the kernel to enable WERROR with W=1 (building KVM
with -Werror is desirable (with a sane compiler) as W=1 does generate
useful warnings).

Opportunistically drop the dependency on !COMPILE_TEST as it's completely
meaningless (it was copied from i195's -Werror Kconfig), as the kernel's
WERROR is explicitly *enabled* for COMPILE_TEST=y kernel's, i.e. enabling
-Werror is obviosly not dependent on COMPILE_TEST=n.

Reported-by: Jakub Kicinski <kuba@kernel.org>
Link: https://lore.kernel.org/all/20231006205415.3501535-1-kuba@kernel.org
Signed-off-by: Sean Christopherson <seanjc@google.com>
---
 arch/x86/kvm/Kconfig | 14 +++++++-------
 1 file changed, 7 insertions(+), 7 deletions(-)

diff --git a/arch/x86/kvm/Kconfig b/arch/x86/kvm/Kconfig
index 950c12868d30..6cc0ea9cd91d 100644
--- a/arch/x86/kvm/Kconfig
+++ b/arch/x86/kvm/Kconfig
@@ -65,13 +65,13 @@ config KVM
 
 config KVM_WERROR
 	bool "Compile KVM with -Werror"
-	# KASAN may cause the build to fail due to larger frames
-	default y if X86_64 && !KASAN
-	# We use the dependency on !COMPILE_TEST to not be enabled
-	# blindly in allmodconfig or allyesconfig configurations
-	depends on KVM
-	depends on (X86_64 && !KASAN) || !COMPILE_TEST
-	depends on EXPERT
+	# Disallow KVM's -Werror if KASAN is enabled, e.g. to guard against
+	# randomized configs from selecting KVM_WERROR=y, which doesn't play
+	# nice with KASAN.  KASAN builds generates warnings for the default
+	# FRAME_WARN, i.e. KVM_WERROR=y with KASAN=y requires special tuning.
+	# Building KVM with -Werror and KASAN is still doable via enabling
+	# the kernel-wide WERROR=y.
+	depends on KVM && EXPERT && !KASAN
 	help
 	  Add -Werror to the build flags for KVM.
 

base-commit: 437bba5ad2bba00c2056c896753a32edf80860cc
-- 
2.42.0.655.g421f12c284-goog

Re: [PATCH] KVM: x86: Turn off KVM_WERROR by default for all configs

[Sean Christopherson]

On Wed, 18 Oct 2023 08:19:06 -0700, Sean Christopherson wrote:
> Don't enable KVM_WERROR by default for x86-64 builds as KVM's one-off
> -Werror enabling is *mostly* superseded by the kernel-wide WERROR, and
> enabling KVM_WERROR by default can cause problems for developers working
> on other subsystems.  E.g. subsystems that have a "zero W=1 regressions"
> rule can inadvertently build KVM with -Werror and W=1, and end up with
> build failures that are completely uninteresting to the developer (W=1 is
> prone to false positives, especially on older compilers).
> 
> [...]

Applied to kvm-x86 misc, thanks!

[1/1] KVM: x86: Turn off KVM_WERROR by default for all configs
      https://github.com/kvm-x86/linux/commit/75bedc1ee90b

--
https://github.com/kvm-x86/linux/tree/next