On Thu, Sep 30, 2021 at 4:13 PM Daniel Axtens <d...@axtens.net> wrote: > > Hi Michael, > > > kvmppc_h_set_dabr(), and kvmppc_h_set_xdabr() which jumps into > > it, need to use _GLOBAL_TOC to setup the kernel TOC pointer, because > > kvmppc_h_set_dabr() uses LOAD_REG_ADDR() to load dawr_force_enable. > > This makes sense. LOAD_REG_ADDR() does ld reg,name@got(r2) and > _GLOBAL_TOC sets r2 based on r12 and .TOC. . > > Looking at > e.g. https://www.mail-archive.com/linux-kernel@vger.kernel.org/msg1610846.html > it seems that we use GOT and TOC largely interchangeably... so assuming > I haven't completely misunderstood, the change this patch makes seems to > make sense to me. :) > > > When called from hcall_try_real_mode() we have the kernel TOC in r2, > > established near the start of kvmppc_interrupt_hv(), so there is no > > issue. > > > > But they can also be called from kvmppc_pseries_do_hcall() which is > > module code, so the access ends up happening with the kvm-hv module's > > r2, which will not point at dawr_force_enable and could even cause a > > fault. > > I checked and there isn't anywhere else the functions are called, so > this will now cover everything. > > > With the current code layout and compilers we haven't observed a fault > > in practice, the load hits somewhere in kvm-hv.ko and silently returns > > some bogus value. > > > > Note that we we expect p8/p9 guests to use the DAWR, but SLOF uses > > h_set_dabr() to test if sc1 works correctly, see SLOF's > > lib/libhvcall/brokensc1.c. > > I assume that something (the module loader?) patches the callsite to > restore r2 after the function call? I imagine something must otherwise > things would fall apart pretty quickly... > > > Fixes: c1fe190c0672 ("powerpc: Add force enable of DAWR on P9 option") > > That patch seems to only affect the DA_W_R not the DA_B_R - how does it > cause this bug?
Isn't it that patch which adds the LOAD_REG_ADDR(r11, dawr_force_enable) to kvmppc_h_set_dabr() which is the problem? > > All in all this looks good to me: > Reviewed-by: Daniel Axtens <d...@axtens.net> > > Kind regards, > Daniel > > > Signed-off-by: Michael Ellerman <m...@ellerman.id.au> > > --- > > arch/powerpc/kvm/book3s_hv_rmhandlers.S | 4 ++-- > > 1 file changed, 2 insertions(+), 2 deletions(-) > > > > diff --git a/arch/powerpc/kvm/book3s_hv_rmhandlers.S > > b/arch/powerpc/kvm/book3s_hv_rmhandlers.S > > index 90484425a1e6..30a8a07cff18 100644 > > --- a/arch/powerpc/kvm/book3s_hv_rmhandlers.S > > +++ b/arch/powerpc/kvm/book3s_hv_rmhandlers.S > > @@ -1999,7 +1999,7 @@ END_FTR_SECTION_IFSET(CPU_FTR_ARCH_300) > > .globl hcall_real_table_end > > hcall_real_table_end: > > > > -_GLOBAL(kvmppc_h_set_xdabr) > > +_GLOBAL_TOC(kvmppc_h_set_xdabr) > > EXPORT_SYMBOL_GPL(kvmppc_h_set_xdabr) > > andi. r0, r5, DABRX_USER | DABRX_KERNEL > > beq 6f > > @@ -2009,7 +2009,7 @@ EXPORT_SYMBOL_GPL(kvmppc_h_set_xdabr) > > 6: li r3, H_PARAMETER > > blr > > > > -_GLOBAL(kvmppc_h_set_dabr) > > +_GLOBAL_TOC(kvmppc_h_set_dabr) > > EXPORT_SYMBOL_GPL(kvmppc_h_set_dabr) > > li r5, DABRX_USER | DABRX_KERNEL > > 3: > > -- > > 2.25.1
