On 24/06/20 21:58, Nadav Amit wrote: >> On Jun 24, 2020, at 7:14 AM, Paolo Bonzini <pbonzini@xxxxxxxxxx> wrote: >> >> The base of the percpu area is stored in the %gs base, and writing >> to %gs destroys it. Move setup_segments earlier, before the %gs >> base is written. >> >> Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx> >> --- >> x86/cstart.S | 2 +- >> 1 file changed, 1 insertion(+), 1 deletion(-) >> >> diff --git a/x86/cstart.S b/x86/cstart.S >> index 5ad70b5..77dc34d 100644 >> --- a/x86/cstart.S >> +++ b/x86/cstart.S >> @@ -106,6 +106,7 @@ MSR_GS_BASE = 0xc0000101 >> .globl start >> start: >> mov $stacktop, %esp >> + setup_segments >> push %ebx >> call setup_multiboot >> call setup_libcflat >> @@ -118,7 +119,6 @@ start: >> >> prepare_32: >> lgdtl gdt32_descr >> - setup_segments >> >> mov %cr4, %eax >> bts $4, %eax // pse >> — >> 2.26.2 > > As I said in a different thread, this change breaks my setup. It is better > not to make any assumption (or as few as possible) about the GDT content > after boot and load the GDTR before setting up the segments. So I prefer to > load the GDT before the segments. How about this change instead of yours? Yes, this is better. Paolo > -- >8 -- > > From: Nadav Amit <namit@xxxxxxxxxx> > Date: Wed, 24 Jun 2020 19:50:36 +0000 > Subject: [PATCH] x86: load gdt while loading segments > > Signed-off-by: Nadav Amit <namit@xxxxxxxxxx> > --- > x86/cstart.S | 7 ++++--- > 1 file changed, 4 insertions(+), 3 deletions(-) > > diff --git a/x86/cstart.S b/x86/cstart.S > index dd33d4d..1d8b8ac 100644 > --- a/x86/cstart.S > +++ b/x86/cstart.S > @@ -95,6 +95,8 @@ MSR_GS_BASE = 0xc0000101 > .endm > > .macro setup_segments > + lgdtl gdt32_descr > + > mov $0x10, %ax > mov %ax, %ds > mov %ax, %es > @@ -106,6 +108,8 @@ MSR_GS_BASE = 0xc0000101 > .globl start > start: > mov $stacktop, %esp > + setup_segments > + > push %ebx > call setup_multiboot > call setup_libcflat > @@ -117,9 +121,6 @@ start: > jmpl $8, $start32 > > prepare_32: > - lgdtl gdt32_descr > - setup_segments > - > mov %cr4, %eax > bts $4, %eax // pse > mov %eax, %cr4 >
