Re: [Xen-devel] [PATCH 5/6] x86/boot: Don't map 0 during boot

2020-01-07 Thread Andrew Cooper
On 07/01/2020 16:35, Jan Beulich wrote: > On 06.01.2020 16:54, Andrew Cooper wrote: >> --- a/xen/arch/x86/boot/head.S >> +++ b/xen/arch/x86/boot/head.S >> @@ -689,12 +689,15 @@ trampoline_setup: >> sub $(L2_PAGETABLE_ENTRIES*8),%eax >> loop1b >> >> -/* >> -

Re: [Xen-devel] [PATCH 5/6] x86/boot: Don't map 0 during boot

2020-01-07 Thread Jan Beulich
On 06.01.2020 16:54, Andrew Cooper wrote: > --- a/xen/arch/x86/boot/head.S > +++ b/xen/arch/x86/boot/head.S > @@ -689,12 +689,15 @@ trampoline_setup: > sub $(L2_PAGETABLE_ENTRIES*8),%eax > loop1b > > -/* > - * During boot, hook 4kB mappings of first 2MB o

[Xen-devel] [PATCH 5/6] x86/boot: Don't map 0 during boot

2020-01-06 Thread Andrew Cooper
In particular, it causes accidental NULL pointer dereferences to go unnoticed. The majority of the early operation takes place either in Real mode, or Protected Unpaged mode. The only bit which requires pagetable mappings is the trampoline transition into Long mode and jump to the higher mappings