Re: [PATCH] x86/asm: Move native_write_cr0/3() out of line

[Peter Zijlstra]

On Wed, Jul 10, 2019 at 09:42:46PM +0200, Thomas Gleixner wrote:
> The pinning of sensitive CR0 and CR4 bits caused a boot crash when loading
> the kvm_intel module on a kernel compiled with CONFIG_PARAVIRT=n.
> 
> The reason is that the static key which controls the pinning is marked RO
> after init. The kvm_intel module contains a CR4 write which requires to
> update the static key entry list. That obviously does not work when the key
> is in a RO section.
> 
> With CONFIG_PARAVIRT enabled this does not happen because the CR4 write
> uses the paravirt indirection and the actual write function is built in.
> 
> As the key is intended to be immutable after init, move
> native_write_cr0/3() out of line.
> 
> While at it consolidate the update of the cr4 shadow variable and store the
> value right away when the pinning is initialized on a booting CPU. No point
> in reading it back 20 instructions later. This allows to confine the static
> key and the pinning variable to cpu/common and allows to mark them static.
> 
> Fixes: 8dbec27a242c ("x86/asm: Pin sensitive CR0 bits")
> Fixes: 873d50d58f67 ("x86/asm: Pin sensitive CR4 bits")
> Reported-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
> Reported-by: Xi Ruoyao <xry111@xxxxxxxxxxxxxxxx>
> Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
> Tested-by: Xi Ruoyao <xry111@xxxxxxxxxxxxxxxx>

Acked-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>