Xen, being 64bit only these days, has no use for a 32bit Ring 0 code segment.
Delete __HYPERVISOR_CS32 and remove it from the GDTs. Also delete
__HYPERVISOR_CS64 and use __HYPERVISOR_CS uniformly.
Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
---
CC: Jan Beulich <JBeulich@suse.com>
CC: Wei Liu <wl@xen.org>
CC: Roger Pau Monné <roger.pau@citrix.com>
---
xen/arch/x86/acpi/wakeup_prot.S | 2 +-
xen/arch/x86/boot/x86_64.S | 2 +-
xen/arch/x86/desc.c | 12 ++++--------
xen/include/asm-x86/config.h | 4 +---
xen/include/asm-x86/desc.h | 4 ++--
5 files changed, 9 insertions(+), 15 deletions(-)
diff --git a/xen/arch/x86/acpi/wakeup_prot.S b/xen/arch/x86/acpi/wakeup_prot.S
index 4a92627436..9e9fcc1ab6 100644
--- a/xen/arch/x86/acpi/wakeup_prot.S
+++ b/xen/arch/x86/acpi/wakeup_prot.S
@@ -74,7 +74,7 @@ ENTRY(__ret_point)
LOAD_GREG(sp)
/* Reload code selector */
- pushq $(__HYPERVISOR_CS64)
+ pushq $__HYPERVISOR_CS
leaq 1f(%rip),%rax
pushq %rax
lretq
diff --git a/xen/arch/x86/boot/x86_64.S b/xen/arch/x86/boot/x86_64.S
index f762dfea11..5ab24d73fc 100644
--- a/xen/arch/x86/boot/x86_64.S
+++ b/xen/arch/x86/boot/x86_64.S
@@ -23,7 +23,7 @@ ENTRY(__high_start)
popf
/* Reload code selector. */
- pushq $(__HYPERVISOR_CS64)
+ pushq $__HYPERVISOR_CS
leaq 1f(%rip),%rax
pushq %rax
lretq
diff --git a/xen/arch/x86/desc.c b/xen/arch/x86/desc.c
index b5c9208164..7d9940d08a 100644
--- a/xen/arch/x86/desc.c
+++ b/xen/arch/x86/desc.c
@@ -31,7 +31,7 @@ __section(".data.page_aligned") __aligned(PAGE_SIZE)
seg_desc_t boot_gdt[PAGE_SIZE / sizeof(seg_desc_t)] =
{
/* 0xe008 - Ring 0 code, 64bit mode */
- [SEL2GDT(__HYPERVISOR_CS64)] = { 0x00af9b000000ffff },
+ [SEL2GDT(__HYPERVISOR_CS)] = { 0x00af9b000000ffff },
/* 0xe010 - Ring 0 data */
[SEL2GDT(__HYPERVISOR_DS32)] = { 0x00cf93000000ffff },
@@ -47,9 +47,7 @@ seg_desc_t boot_gdt[PAGE_SIZE / sizeof(seg_desc_t)] =
/* 0xe033 - Ring 3 code, 64-bit mode */
[SEL2GDT(FLAT_RING3_CS64)] = { 0x00affb000000ffff },
- /* 0xe038 - Ring 0 code, compatibility */
- [SEL2GDT(__HYPERVISOR_CS32)] = { 0x00cf9b000000ffff },
-
+ /* 0xe038 - reserved */
/* 0xe040 - TSS */
/* 0xe050 - LDT */
@@ -61,7 +59,7 @@ __section(".data.page_aligned") __aligned(PAGE_SIZE)
seg_desc_t boot_compat_gdt[PAGE_SIZE / sizeof(seg_desc_t)] =
{
/* 0xe008 - Ring 0 code, 64bit mode */
- [SEL2GDT(__HYPERVISOR_CS64)] = { 0x00af9b000000ffff },
+ [SEL2GDT(__HYPERVISOR_CS)] = { 0x00af9b000000ffff },
/* 0xe010 - Ring 0 data */
[SEL2GDT(__HYPERVISOR_DS32)] = { 0x00cf93000000ffff },
@@ -78,9 +76,7 @@ seg_desc_t boot_compat_gdt[PAGE_SIZE / sizeof(seg_desc_t)] =
/* 0xe033 - Ring 3 data */
[SEL2GDT(FLAT_COMPAT_RING3_DS)] = { 0x00cff3000000ffff },
- /* 0xe038 - Ring 0 code, compatibility */
- [SEL2GDT(__HYPERVISOR_CS32)] = { 0x00cf9b000000ffff },
-
+ /* 0xe038 - reserved */
/* 0xe040 - TSS */
/* 0xe050 - LDT */
diff --git a/xen/include/asm-x86/config.h b/xen/include/asm-x86/config.h
index 6e4f28d934..22dc795eea 100644
--- a/xen/include/asm-x86/config.h
+++ b/xen/include/asm-x86/config.h
@@ -264,9 +264,7 @@ extern unsigned char boot_edid_info[128];
#endif
-#define __HYPERVISOR_CS64 0xe008
-#define __HYPERVISOR_CS32 0xe038
-#define __HYPERVISOR_CS __HYPERVISOR_CS64
+#define __HYPERVISOR_CS 0xe008
#define __HYPERVISOR_DS64 0x0000
#define __HYPERVISOR_DS32 0xe010
#define __HYPERVISOR_DS __HYPERVISOR_DS64
diff --git a/xen/include/asm-x86/desc.h b/xen/include/asm-x86/desc.h
index 80aa254206..4b29dac259 100644
--- a/xen/include/asm-x86/desc.h
+++ b/xen/include/asm-x86/desc.h
@@ -155,7 +155,7 @@ do { \
((unsigned long)(dpl) << 45) | \
((unsigned long)(type) << 40) | \
((unsigned long)(addr) & 0xFFFFUL) | \
- ((unsigned long)__HYPERVISOR_CS64 << 16) | \
+ ((unsigned long)__HYPERVISOR_CS << 16) | \
(1UL << 47); \
} while (0)
@@ -169,7 +169,7 @@ static inline void _set_gate_lower(idt_entry_t *gate, unsigned long type,
((unsigned long)(dpl) << 45) |
((unsigned long)(type) << 40) |
((unsigned long)(addr) & 0xFFFFUL) |
- ((unsigned long)__HYPERVISOR_CS64 << 16) |
+ ((unsigned long)__HYPERVISOR_CS << 16) |
(1UL << 47);
_write_gate_lower(gate, &idte);
}
--
2.11.0
_______________________________________________
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Xen-devel@lists.xenproject.org
https://lists.xenproject.org/mailman/listinfo/xen-develOn 09.08.2019 14:39, Andrew Cooper wrote: > Xen, being 64bit only these days, has no use for a 32bit Ring 0 code segment. > > Delete __HYPERVISOR_CS32 and remove it from the GDTs. Also delete > __HYPERVISOR_CS64 and use __HYPERVISOR_CS uniformly. Long, long ago we've been considering doing this. Agreed, nothing has surfaced to actually use it, but I wouldn't subscribe to "has no use": We will need it if we ever want to be able to run on 32-bit EFI _and_ invoke runtime services there. Back then through the consideration against dropping it was that we may want to invoke 32-bit BIOS services (PCI, VGA) from the hypervisor. Of course it wouldn't be terribly difficult to re-instate these selectors / descriptors, but still. Nevertheless, if you're convinced of the move despite the remarks above ... > Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com> Acked-by: Jan Beulich <jbeulich@suse.com> Jan _______________________________________________ Xen-devel mailing list Xen-devel@lists.xenproject.org https://lists.xenproject.org/mailman/listinfo/xen-devel
On 09/08/2019 13:50, Jan Beulich wrote: > On 09.08.2019 14:39, Andrew Cooper wrote: >> Xen, being 64bit only these days, has no use for a 32bit Ring 0 code >> segment. >> >> Delete __HYPERVISOR_CS32 and remove it from the GDTs. Also delete >> __HYPERVISOR_CS64 and use __HYPERVISOR_CS uniformly. > > Long, long ago we've been considering doing this. Agreed, > nothing has surfaced to actually use it, but I wouldn't > subscribe to "has no use": We will need it if we ever want > to be able to run on 32-bit EFI _and_ invoke runtime > services there. Back then through the consideration against > dropping it was that we may want to invoke 32-bit BIOS > services (PCI, VGA) from the hypervisor. I hadn't realised these had even been considered in the past. I don't think either of these are likely to happen now. As for the text, Xen really does have no users of a 32bit R0 code segment, and the statement does not preclude the fact that there may be legitimate uses for CS32. Would you be happier with "days, and does not use a 32bit Ring 0 code segment." ? There is specifically a good reason for taking it out (given that it isn't used), to avoid cascade breakage from a stray far jump which happens to start executing code in the wrong mode. ~Andrew _______________________________________________ Xen-devel mailing list Xen-devel@lists.xenproject.org https://lists.xenproject.org/mailman/listinfo/xen-devel
On 09.08.2019 17:36, Andrew Cooper wrote: > On 09/08/2019 13:50, Jan Beulich wrote: >> On 09.08.2019 14:39, Andrew Cooper wrote: >>> Xen, being 64bit only these days, has no use for a 32bit Ring 0 code >>> segment. >>> >>> Delete __HYPERVISOR_CS32 and remove it from the GDTs. Also delete >>> __HYPERVISOR_CS64 and use __HYPERVISOR_CS uniformly. >> >> Long, long ago we've been considering doing this. Agreed, >> nothing has surfaced to actually use it, but I wouldn't >> subscribe to "has no use": We will need it if we ever want >> to be able to run on 32-bit EFI _and_ invoke runtime >> services there. Back then through the consideration against >> dropping it was that we may want to invoke 32-bit BIOS >> services (PCI, VGA) from the hypervisor. > > I hadn't realised these had even been considered in the past. I don't > think either of these are likely to happen now. > > As for the text, Xen really does have no users of a 32bit R0 code > segment, and the statement does not preclude the fact that there may be > legitimate uses for CS32. > > Would you be happier with "days, and does not use a 32bit Ring 0 code > segment." ? Yes, "does not use" is definitely more correct imo, as would be "has no user" (note the extra "r" compared to your original text; your reply makes me wonder whether it was simply a typo). Jan _______________________________________________ Xen-devel mailing list Xen-devel@lists.xenproject.org https://lists.xenproject.org/mailman/listinfo/xen-devel
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