arm64: mm: limit linear region to 51 bits for KVM in nVHE mode
RFC PATCH 1/1 arm64: mm: limit linear region to 51 bits for KVM in nVHE mode
KVM in nVHE mode divides up its VA space into two equal halves, and picks the half that does not conflict with the HYP ID map to map its linear region. This worked fine when the kernel's linear map itself was guaranteed to cover precisely as many bits of VA space, but this was changed by commit f4693c2716b35d08 ("arm64: mm: extend linear region for 52-bit VA configurations").
The result is that, depending on the placement of the ID map, kernel-VA to hyp-VA translations may produce addresses that either conflict with other HYP mappings (including the ID map itself) or generate addresses outside of the 52-bit addressable range, neither of which is likely to lead to anything useful.
Given that 52-bit capable cores are guaranteed to implement VHE, this only affects configurations such as pKVM where we opt into non-VHE mode even if the hardware is VHE capable. So just for these configurations, let's limit the kernel linear map to 51 bits and work around the problem.
---
NOTE: build tested only
arch/arm64/mm/init.c | 16 +++++++++++++++- 1 file changed, 15 insertions(+), 1 deletion(-)
arch/arm64/mm/init.c +15 -1
@@ -282,7 +282,21 @@ static void __init fdt_enforce_memory_region(void)void __init arm64_memblock_init (void ) { -const s64 linear_region_size =PAGE_END -_PAGE_OFFSET (vabits_actual); +s64 linear_region_size =PAGE_END -_PAGE_OFFSET (vabits_actual); + +/* +* Corner case: 52-bit VA capable systems running KVM in nVHE mode may +* be limited in their ability to support a linear map that exceeds 51 +* bits of VA space, depending on the placement of the ID map. Given +* that the placement of the ID map may be randomized, let's simply +* limit the kernel's linear map to 51 bits as well if we detect this +* configuration. +*/ +if (IS_ENABLED (CONFIG_KVM ) && vabits_actual ==52 && + !is_kernel_in_hyp_mode ()) { +pr_info ("Capping linear region to 51 bits for KVM in nVHE mode on LVA capable hardware.\n" ); + linear_region_size =BIT (51 ); + }/* Handle linux,usable-memory-range property */ fdt_enforce_memory_region ();
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2.20.1 _______________________________________________ linux-arm-kernel mailing list [email protected] http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
Will Deacon
maintainerQuoted 41 lines · Ard Biesheuvel
KVM in nVHE mode divides up its VA space into two equal halves, and picks the half that does not conflict with the HYP ID map to map its linear region. This worked fine when the kernel's linear map itself was guaranteed to cover precisely as many bits of VA space, but this was changed by commit
f4693c2716b35d08("arm64: mm: extend linear region for 52-bit VA configurations").The result is that, depending on the placement of the ID map, kernel-VA to hyp-VA translations may produce addresses that either conflict with other HYP mappings (including the ID map itself) or generate addresses outside of the 52-bit addressable range, neither of which is likely to lead to anything useful.
Given that 52-bit capable cores are guaranteed to implement VHE, this only affects configurations such as pKVM where we opt into non-VHE mode even if the hardware is VHE capable. So just for these configurations, let's limit the kernel linear map to 51 bits and work around the problem.
Fixes f4693c2716b35d08 ("arm64: mm: extend linear region for 52-bit VA configurations")Signed-off-by Ard Biesheuvel <[email protected]>---
NOTE: build tested onlyarch/arm64/mm/init.c | 16 +++++++++++++++- 1 file changed, 15 insertions(+), 1 deletion(-)arch/arm64/mm/init.c +5
-1@@ -282,7 +282,21 @@ static void __init fdt_enforce_memory_region(void)void __init arm64_memblock_init (void ) { -const s64 linear_region_size =PAGE_END -_PAGE_OFFSET (vabits_actual); +s64 linear_region_size =PAGE_END -_PAGE_OFFSET (vabits_actual); + +/* +* Corner case: 52-bit VA capable systems running KVM in nVHE mode may +* be limited in their ability to support a linear map that exceeds 51
arch/arm64/mm/init.c static void __init fdt_enforce_memory_region(void) · line 299
Quoted 10 lines
arch/arm64/mm/init.c +10
-0+* bits of VA space, depending on the placement of the ID map. Given +* that the placement of the ID map may be randomized, let's simply +* limit the kernel's linear map to 51 bits as well if we detect this +* configuration. +*/ +if (IS_ENABLED (CONFIG_KVM ) && vabits_actual ==52 && + !is_kernel_in_hyp_mode ()) { +pr_info ("Capping linear region to 51 bits for KVM in nVHE mode on LVA capable hardware.\n" ); + linear_region_size =BIT (51 ); + }
Slight nit, but to avoid having to think about PAGE_END I think this would be a little clearer as:
if (IS_ENABLED(CONFIG_KVM) && !is_kernel_in_hyp_mode()) linear_region_size = min_t(u64, linear_region_size, BIT(51));
Will
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Quoted 57 lines · Will Deacon
Quoted 41 lines · Ard Biesheuvel
KVM in nVHE mode divides up its VA space into two equal halves, and picks the half that does not conflict with the HYP ID map to map its linear region. This worked fine when the kernel's linear map itself was guaranteed to cover precisely as many bits of VA space, but this was changed by commit
f4693c2716b35d08("arm64: mm: extend linear region for 52-bit VA configurations").The result is that, depending on the placement of the ID map, kernel-VA to hyp-VA translations may produce addresses that either conflict with other HYP mappings (including the ID map itself) or generate addresses outside of the 52-bit addressable range, neither of which is likely to lead to anything useful.
Given that 52-bit capable cores are guaranteed to implement VHE, this only affects configurations such as pKVM where we opt into non-VHE mode even if the hardware is VHE capable. So just for these configurations, let's limit the kernel linear map to 51 bits and work around the problem.
Fixes f4693c2716b35d08 ("arm64: mm: extend linear region for 52-bit VA configurations")Signed-off-by Ard Biesheuvel <[email protected]>---
NOTE: build tested onlyarch/arm64/mm/init.c | 16 +++++++++++++++- 1 file changed, 15 insertions(+), 1 deletion(-)arch/arm64/mm/init.c +5
-1@@ -282,7 +282,21 @@ static void __init fdt_enforce_memory_region(void)void __init arm64_memblock_init (void ) { -const s64 linear_region_size =PAGE_END -_PAGE_OFFSET (vabits_actual); +s64 linear_region_size =PAGE_END -_PAGE_OFFSET (vabits_actual); + +/* +* Corner case: 52-bit VA capable systems running KVM in nVHE mode may +* be limited in their ability to support a linear map that exceeds 51 arch/arm64/mm/init.c static void __init fdt_enforce_memory_region(void) · line 299
Quoted 10 lines
arch/arm64/mm/init.c +10
-0+* bits of VA space, depending on the placement of the ID map. Given +* that the placement of the ID map may be randomized, let's simply +* limit the kernel's linear map to 51 bits as well if we detect this +* configuration. +*/ +if (IS_ENABLED (CONFIG_KVM ) && vabits_actual ==52 && + !is_kernel_in_hyp_mode ()) { +pr_info ("Capping linear region to 51 bits for KVM in nVHE mode on LVA capable hardware.\n" ); + linear_region_size =BIT (51 ); + }Slight nit, but to avoid having to think about
PAGE_ENDI think this would be a little clearer as:
Quoted 3 lines
if (IS_ENABLED(CONFIG_KVM) && !is_kernel_in_hyp_mode())
linear_region_size = min_t(u64, linear_region_size, BIT(51));Fair enough.
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Catalin Marinas
maintainerQuoted 30 lines · Ard Biesheuvel
Quoted 29 lines · Will Deacon
Quoted 14 lines · Ard Biesheuvel
arch/arm64/mm/init.c +5
-1@@ -282,7 +282,21 @@ static void __init fdt_enforce_memory_region(void)void __init arm64_memblock_init (void ) { -const s64 linear_region_size =PAGE_END -_PAGE_OFFSET (vabits_actual); +s64 linear_region_size =PAGE_END -_PAGE_OFFSET (vabits_actual); + +/* +* Corner case: 52-bit VA capable systems running KVM in nVHE mode may +* be limited in their ability to support a linear map that exceeds 51 arch/arm64/mm/init.c static void __init fdt_enforce_memory_region(void) · line 299
Quoted 10 lines
arch/arm64/mm/init.c +10
-0+* bits of VA space, depending on the placement of the ID map. Given +* that the placement of the ID map may be randomized, let's simply +* limit the kernel's linear map to 51 bits as well if we detect this +* configuration. +*/ +if (IS_ENABLED (CONFIG_KVM ) && vabits_actual ==52 && + !is_kernel_in_hyp_mode ()) { +pr_info ("Capping linear region to 51 bits for KVM in nVHE mode on LVA capable hardware.\n" ); + linear_region_size =BIT (51 ); + }Slight nit, but to avoid having to think about
PAGE_ENDI think this would be a little clearer as:
Quoted 5 lines
Quoted 3 lines
if (IS_ENABLED(CONFIG_KVM) && !is_kernel_in_hyp_mode()) linear_region_size = min_t(u64, linear_region_size, BIT(51));Fair enough.
Ard, do you plan to post a new version? I can make the change myself locally as well.
Signature · 6 lines
Catalin _______________________________________________ linux-arm-kernel mailing list [email protected] http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
Quoted 32 lines · Catalin Marinas
Quoted 30 lines · Ard Biesheuvel
Quoted 29 lines · Will Deacon
Quoted 14 lines · Ard Biesheuvel
arch/arm64/mm/init.c +5
-1@@ -282,7 +282,21 @@ static void __init fdt_enforce_memory_region(void)void __init arm64_memblock_init (void ) { -const s64 linear_region_size =PAGE_END -_PAGE_OFFSET (vabits_actual); +s64 linear_region_size =PAGE_END -_PAGE_OFFSET (vabits_actual); + +/* +* Corner case: 52-bit VA capable systems running KVM in nVHE mode may +* be limited in their ability to support a linear map that exceeds 51 arch/arm64/mm/init.c static void __init fdt_enforce_memory_region(void) · line 299
Quoted 10 lines
arch/arm64/mm/init.c +10
-0+* bits of VA space, depending on the placement of the ID map. Given +* that the placement of the ID map may be randomized, let's simply +* limit the kernel's linear map to 51 bits as well if we detect this +* configuration. +*/ +if (IS_ENABLED (CONFIG_KVM ) && vabits_actual ==52 && + !is_kernel_in_hyp_mode ()) { +pr_info ("Capping linear region to 51 bits for KVM in nVHE mode on LVA capable hardware.\n" ); + linear_region_size =BIT (51 ); + }Slight nit, but to avoid having to think about
PAGE_ENDI think this would be a little clearer as:
Quoted 9 lines
Quoted 5 lines
Quoted 3 lines
if (IS_ENABLED(CONFIG_KVM) && !is_kernel_in_hyp_mode()) linear_region_size = min_t(u64, linear_region_size, BIT(51));Fair enough.
Ard, do you plan to post a new version? I can make the change myself locally as well.
If you don't mind doing so, please go ahead.
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Catalin Marinas
maintainerQuoted 56 lines · Will Deacon
Quoted 41 lines · Ard Biesheuvel
KVM in nVHE mode divides up its VA space into two equal halves, and picks the half that does not conflict with the HYP ID map to map its linear region. This worked fine when the kernel's linear map itself was guaranteed to cover precisely as many bits of VA space, but this was changed by commit
f4693c2716b35d08("arm64: mm: extend linear region for 52-bit VA configurations").The result is that, depending on the placement of the ID map, kernel-VA to hyp-VA translations may produce addresses that either conflict with other HYP mappings (including the ID map itself) or generate addresses outside of the 52-bit addressable range, neither of which is likely to lead to anything useful.
Given that 52-bit capable cores are guaranteed to implement VHE, this only affects configurations such as pKVM where we opt into non-VHE mode even if the hardware is VHE capable. So just for these configurations, let's limit the kernel linear map to 51 bits and work around the problem.
Fixes f4693c2716b35d08 ("arm64: mm: extend linear region for 52-bit VA configurations")Signed-off-by Ard Biesheuvel <[email protected]>---
NOTE: build tested onlyarch/arm64/mm/init.c | 16 +++++++++++++++- 1 file changed, 15 insertions(+), 1 deletion(-)arch/arm64/mm/init.c +5
-1@@ -282,7 +282,21 @@ static void __init fdt_enforce_memory_region(void)void __init arm64_memblock_init (void ) { -const s64 linear_region_size =PAGE_END -_PAGE_OFFSET (vabits_actual); +s64 linear_region_size =PAGE_END -_PAGE_OFFSET (vabits_actual); + +/* +* Corner case: 52-bit VA capable systems running KVM in nVHE mode may +* be limited in their ability to support a linear map that exceeds 51 arch/arm64/mm/init.c static void __init fdt_enforce_memory_region(void) · line 299
Quoted 10 lines
arch/arm64/mm/init.c +10
-0+* bits of VA space, depending on the placement of the ID map. Given +* that the placement of the ID map may be randomized, let's simply +* limit the kernel's linear map to 51 bits as well if we detect this +* configuration. +*/ +if (IS_ENABLED (CONFIG_KVM ) && vabits_actual ==52 && + !is_kernel_in_hyp_mode ()) { +pr_info ("Capping linear region to 51 bits for KVM in nVHE mode on LVA capable hardware.\n" ); + linear_region_size =BIT (51 ); + }Slight nit, but to avoid having to think about
PAGE_ENDI think this would be a little clearer as:
Quoted 2 lines
if (IS_ENABLED(CONFIG_KVM) && !is_kernel_in_hyp_mode()) linear_region_size = min_t(u64, linear_region_size, BIT(51));
BTW, do we also need to check is_hyp_mode_available() (instead of just CONFIG_KVM)? We don't need this reduction for a guest.
Signature · 6 lines
Catalin _______________________________________________ linux-arm-kernel mailing list [email protected] http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
Quoted 58 lines · Catalin Marinas
Quoted 56 lines · Will Deacon
Quoted 41 lines · Ard Biesheuvel
KVM in nVHE mode divides up its VA space into two equal halves, and picks the half that does not conflict with the HYP ID map to map its linear region. This worked fine when the kernel's linear map itself was guaranteed to cover precisely as many bits of VA space, but this was changed by commit
f4693c2716b35d08("arm64: mm: extend linear region for 52-bit VA configurations").The result is that, depending on the placement of the ID map, kernel-VA to hyp-VA translations may produce addresses that either conflict with other HYP mappings (including the ID map itself) or generate addresses outside of the 52-bit addressable range, neither of which is likely to lead to anything useful.
Given that 52-bit capable cores are guaranteed to implement VHE, this only affects configurations such as pKVM where we opt into non-VHE mode even if the hardware is VHE capable. So just for these configurations, let's limit the kernel linear map to 51 bits and work around the problem.
Fixes f4693c2716b35d08 ("arm64: mm: extend linear region for 52-bit VA configurations")Signed-off-by Ard Biesheuvel <[email protected]>---
NOTE: build tested onlyarch/arm64/mm/init.c | 16 +++++++++++++++- 1 file changed, 15 insertions(+), 1 deletion(-)arch/arm64/mm/init.c +5
-1@@ -282,7 +282,21 @@ static void __init fdt_enforce_memory_region(void)void __init arm64_memblock_init (void ) { -const s64 linear_region_size =PAGE_END -_PAGE_OFFSET (vabits_actual); +s64 linear_region_size =PAGE_END -_PAGE_OFFSET (vabits_actual); + +/* +* Corner case: 52-bit VA capable systems running KVM in nVHE mode may +* be limited in their ability to support a linear map that exceeds 51 arch/arm64/mm/init.c static void __init fdt_enforce_memory_region(void) · line 299
Quoted 10 lines
arch/arm64/mm/init.c +10
-0+* bits of VA space, depending on the placement of the ID map. Given +* that the placement of the ID map may be randomized, let's simply +* limit the kernel's linear map to 51 bits as well if we detect this +* configuration. +*/ +if (IS_ENABLED (CONFIG_KVM ) && vabits_actual ==52 && + !is_kernel_in_hyp_mode ()) { +pr_info ("Capping linear region to 51 bits for KVM in nVHE mode on LVA capable hardware.\n" ); + linear_region_size =BIT (51 ); + }Slight nit, but to avoid having to think about
PAGE_ENDI think this would be a little clearer as:
Quoted 6 lines
Quoted 2 lines
if (IS_ENABLED(CONFIG_KVM) && !is_kernel_in_hyp_mode()) linear_region_size = min_t(u64, linear_region_size, BIT(51));BTW, do we also need to check
is_hyp_mode_available()(instead of justCONFIG_KVM)? We don't need this reduction for a guest.
Hmm, good point. I'll respin with both suggestions incorporated.
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