| Message ID | 1463052404-18092-1-git-send-email-thuth@redhat.com (mailing list archive) |
|---|---|
| State | Accepted |
| Headers | show |
On Thu, May 12, 2016 at 01:26:44PM +0200, Thomas Huth wrote: > The SIAR and SDAR registers are available twice, one time as SPRs > 780 / 781 (unprivileged, but read-only), and one time as the SPRs > 796 / 797 (privileged, but read and write). The Linux kernel code > currently uses the unprivileged SPRs - while this is OK for reading, > writing to that register of course does not work. > Since the KVM code tries to write to this register, too (see the mtspr > in book3s_hv_rmhandlers.S), the contents of this register sometimes get > lost for the guests, e.g. during migration of a VM. > To fix this issue, simply switch to the privileged SPR numbers instead. > > Signed-off-by: Thomas Huth <thuth@redhat.com> Acked-by: Paul Mackerras <paulus@ozlabs.org>
On 13.05.2016 05:35, Paul Mackerras wrote: > On Thu, May 12, 2016 at 01:26:44PM +0200, Thomas Huth wrote: >> The SIAR and SDAR registers are available twice, one time as SPRs >> 780 / 781 (unprivileged, but read-only), and one time as the SPRs >> 796 / 797 (privileged, but read and write). The Linux kernel code >> currently uses the unprivileged SPRs - while this is OK for reading, >> writing to that register of course does not work. >> Since the KVM code tries to write to this register, too (see the mtspr >> in book3s_hv_rmhandlers.S), the contents of this register sometimes get >> lost for the guests, e.g. during migration of a VM. >> To fix this issue, simply switch to the privileged SPR numbers instead. >> >> Signed-off-by: Thomas Huth <thuth@redhat.com> > > Acked-by: Paul Mackerras <paulus@ozlabs.org> *ping* Michael, could you please pick this patch up? I think it should rather go through the generic powerpc tree instead of kvm-ppc, since it also affects other parts than just KVM... Thanks, Thomas
On Mon, 2016-05-30 at 10:04 +0200, Thomas Huth wrote: > On 13.05.2016 05:35, Paul Mackerras wrote: > > On Thu, May 12, 2016 at 01:26:44PM +0200, Thomas Huth wrote: > > > The SIAR and SDAR registers are available twice, one time as SPRs > > > 780 / 781 (unprivileged, but read-only), and one time as the SPRs > > > 796 / 797 (privileged, but read and write). The Linux kernel code > > > currently uses the unprivileged SPRs - while this is OK for reading, > > > writing to that register of course does not work. > > > Since the KVM code tries to write to this register, too (see the mtspr > > > in book3s_hv_rmhandlers.S), the contents of this register sometimes get > > > lost for the guests, e.g. during migration of a VM. > > > To fix this issue, simply switch to the privileged SPR numbers instead. > > > > > > Signed-off-by: Thomas Huth <thuth@redhat.com> > > > > Acked-by: Paul Mackerras <paulus@ozlabs.org> > > *ping* > > Michael, could you please pick this patch up? I think it should rather > go through the generic powerpc tree instead of kvm-ppc, since it also > affects other parts than just KVM... Yeah that's actually why I hesitated to merge it, because I want to know what the broader implications are ... I have also gone back and confirmed that the 796/797 numbers exist and are correct on all CPUs we support, which involved a lot of digging through PDFs. cheers
On Thu, 2016-12-05 at 11:26:44 UTC, Thomas Huth wrote: > The SIAR and SDAR registers are available twice, one time as SPRs > 780 / 781 (unprivileged, but read-only), and one time as the SPRs > 796 / 797 (privileged, but read and write). The Linux kernel code > currently uses the unprivileged SPRs - while this is OK for reading, > writing to that register of course does not work. > Since the KVM code tries to write to this register, too (see the mtspr > in book3s_hv_rmhandlers.S), the contents of this register sometimes get > lost for the guests, e.g. during migration of a VM. > To fix this issue, simply switch to the privileged SPR numbers instead. > > Signed-off-by: Thomas Huth <thuth@redhat.com> > Acked-by: Paul Mackerras <paulus@ozlabs.org> Applied to powerpc fixes, thanks. https://git.kernel.org/powerpc/c/d23fac2b27d94aeb7b65536a50 cheers
diff --git a/arch/powerpc/include/asm/reg.h b/arch/powerpc/include/asm/reg.h index f5f4c66..ce3e1b7 100644 --- a/arch/powerpc/include/asm/reg.h +++ b/arch/powerpc/include/asm/reg.h @@ -752,13 +752,13 @@ #define SPRN_PMC6 792 #define SPRN_PMC7 793 #define SPRN_PMC8 794 -#define SPRN_SIAR 780 -#define SPRN_SDAR 781 #define SPRN_SIER 784 #define SIER_SIPR 0x2000000 /* Sampled MSR_PR */ #define SIER_SIHV 0x1000000 /* Sampled MSR_HV */ #define SIER_SIAR_VALID 0x0400000 /* SIAR contents valid */ #define SIER_SDAR_VALID 0x0200000 /* SDAR contents valid */ +#define SPRN_SIAR 796 +#define SPRN_SDAR 797 #define SPRN_TACR 888 #define SPRN_TCSCR 889 #define SPRN_CSIGR 890
The SIAR and SDAR registers are available twice, one time as SPRs 780 / 781 (unprivileged, but read-only), and one time as the SPRs 796 / 797 (privileged, but read and write). The Linux kernel code currently uses the unprivileged SPRs - while this is OK for reading, writing to that register of course does not work. Since the KVM code tries to write to this register, too (see the mtspr in book3s_hv_rmhandlers.S), the contents of this register sometimes get lost for the guests, e.g. during migration of a VM. To fix this issue, simply switch to the privileged SPR numbers instead. Signed-off-by: Thomas Huth <thuth@redhat.com> --- arch/powerpc/include/asm/reg.h | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-)