* Re: [PATCH 1/1] x86/boot/compressed/64: Set EFER.LME=1 in 32-bit trampoline code before returning to long mode [not found] ` <20190107082512.w5gkbebsypionyey@black.fi.intel.com> @ 2019-01-07 20:03 ` Wei Huang 2019-01-07 21:53 ` Benjamin Gilbert 0 siblings, 1 reply; 4+ messages in thread From: Wei Huang @ 2019-01-07 20:03 UTC (permalink / raw) To: Kirill A. Shutemov Cc: x86, tglx, mingo, bp, hpa, linux-kernel, linux-x86_64, bgilbert [adding lkml and linux-x86_64] On 1/7/19 2:25 AM, Kirill A. Shutemov wrote: > On Fri, Jan 04, 2019 at 05:44:11AM +0000, Wei Huang wrote: >> In some old AMD KVM implementation, guest's EFER.LME bit is cleared by KVM >> when the hypervsior detects guest sets CR0.PG to 0. This causes guest OS >> to reboot when it tries to return from 32-bit trampoline code because CPU >> is in incorrect state: CR4.PAE=1, CR0.PG=1, CS.L=1, but EFER.LME=0. >> As a precaution, this patch sets EFER.LME=1 as part of long mode >> activation procedure. This extra step won't cause any harm when Linux is >> booting on bare-metal machine. >> >> Signed-off-by: Wei Huang <wei@redhat.com> > > Thanks for tracking this down. BTW I think this patch _might_ be related the recent reboot issue reported in https://lkml.org/lkml/2018/7/1/836 since the symptoms are exactly the same. > > Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> > Fixes: 34bbb0009f3b ("x86/boot/compressed: Enable 5-level paging during decompression stage") > ^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [PATCH 1/1] x86/boot/compressed/64: Set EFER.LME=1 in 32-bit trampoline code before returning to long mode 2019-01-07 20:03 ` [PATCH 1/1] x86/boot/compressed/64: Set EFER.LME=1 in 32-bit trampoline code before returning to long mode Wei Huang @ 2019-01-07 21:53 ` Benjamin Gilbert 2019-01-07 22:02 ` Wei Huang 0 siblings, 1 reply; 4+ messages in thread From: Benjamin Gilbert @ 2019-01-07 21:53 UTC (permalink / raw) To: Wei Huang Cc: Kirill A. Shutemov, x86, tglx, mingo, bp, hpa, linux-kernel, linux-x86_64 On Mon, Jan 07, 2019 at 02:03:15PM -0600, Wei Huang wrote: > On 1/7/19 2:25 AM, Kirill A. Shutemov wrote: > > On Fri, Jan 04, 2019 at 05:44:11AM +0000, Wei Huang wrote: > >> In some old AMD KVM implementation, guest's EFER.LME bit is cleared by KVM > >> when the hypervsior detects guest sets CR0.PG to 0. This causes guest OS > >> to reboot when it tries to return from 32-bit trampoline code because CPU > >> is in incorrect state: CR4.PAE=1, CR0.PG=1, CS.L=1, but EFER.LME=0. > >> As a precaution, this patch sets EFER.LME=1 as part of long mode > >> activation procedure. This extra step won't cause any harm when Linux is > >> booting on bare-metal machine. > >> > >> Signed-off-by: Wei Huang <wei@redhat.com> > > > > Thanks for tracking this down. > > BTW I think this patch _might_ be related the recent reboot issue > reported in https://lkml.org/lkml/2018/7/1/836 since the symptoms are > exactly the same. The problem in that case turned out to be https://lkml.org/lkml/2018/7/4/723 which was fixed by d503ac531a. --Benjamin Gilbert ^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [PATCH 1/1] x86/boot/compressed/64: Set EFER.LME=1 in 32-bit trampoline code before returning to long mode 2019-01-07 21:53 ` Benjamin Gilbert @ 2019-01-07 22:02 ` Wei Huang 0 siblings, 0 replies; 4+ messages in thread From: Wei Huang @ 2019-01-07 22:02 UTC (permalink / raw) To: Benjamin Gilbert Cc: Kirill A. Shutemov, x86, tglx, mingo, bp, hpa, linux-kernel, linux-x86_64 On 1/7/19 3:53 PM, Benjamin Gilbert wrote: > On Mon, Jan 07, 2019 at 02:03:15PM -0600, Wei Huang wrote: >> On 1/7/19 2:25 AM, Kirill A. Shutemov wrote: >>> On Fri, Jan 04, 2019 at 05:44:11AM +0000, Wei Huang wrote: >>>> In some old AMD KVM implementation, guest's EFER.LME bit is cleared by KVM >>>> when the hypervsior detects guest sets CR0.PG to 0. This causes guest OS >>>> to reboot when it tries to return from 32-bit trampoline code because CPU >>>> is in incorrect state: CR4.PAE=1, CR0.PG=1, CS.L=1, but EFER.LME=0. >>>> As a precaution, this patch sets EFER.LME=1 as part of long mode >>>> activation procedure. This extra step won't cause any harm when Linux is >>>> booting on bare-metal machine. >>>> >>>> Signed-off-by: Wei Huang <wei@redhat.com> >>> >>> Thanks for tracking this down. >> >> BTW I think this patch _might_ be related the recent reboot issue >> reported in https://lkml.org/lkml/2018/7/1/836 since the symptoms are >> exactly the same. > > The problem in that case turned out to be https://lkml.org/lkml/2018/7/4/723 > which was fixed by d503ac531a. OK, then it is a different problem. For this specific patch, without it, the latest kernel can't boot on RHEL6 (and other old KVM distros) as a guest VM on AMD box. > > --Benjamin Gilbert > ^ permalink raw reply [flat|nested] 4+ messages in thread
* [tip:x86/urgent] x86/boot/compressed/64: Set EFER.LME=1 in 32-bit trampoline before returning to long mode [not found] <20190104054411.12489-1-wei@redhat.com> [not found] ` <20190107082512.w5gkbebsypionyey@black.fi.intel.com> @ 2019-01-29 21:03 ` tip-bot for Wei Huang 1 sibling, 0 replies; 4+ messages in thread From: tip-bot for Wei Huang @ 2019-01-29 21:03 UTC (permalink / raw) To: linux-tip-commits; +Cc: linux-kernel, mingo, tglx, kirill.shutemov, wei, hpa Commit-ID: b677dfae5aa197afc5191755a76a8727ffca538a Gitweb: https://git.kernel.org/tip/b677dfae5aa197afc5191755a76a8727ffca538a Author: Wei Huang <wei@redhat.com> AuthorDate: Thu, 3 Jan 2019 23:44:11 -0600 Committer: Thomas Gleixner <tglx@linutronix.de> CommitDate: Tue, 29 Jan 2019 21:58:59 +0100 x86/boot/compressed/64: Set EFER.LME=1 in 32-bit trampoline before returning to long mode In some old AMD KVM implementation, guest's EFER.LME bit is cleared by KVM when the hypervsior detects that the guest sets CR0.PG to 0. This causes the guest OS to reboot when it tries to return from 32-bit trampoline code because the CPU is in incorrect state: CR4.PAE=1, CR0.PG=1, CS.L=1, but EFER.LME=0. As a precaution, set EFER.LME=1 as part of long mode activation procedure. This extra step won't cause any harm when Linux is booted on a bare-metal machine. Signed-off-by: Wei Huang <wei@redhat.com> Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com> Cc: bp@alien8.de Cc: hpa@zytor.com Link: https://lkml.kernel.org/r/20190104054411.12489-1-wei@redhat.com --- arch/x86/boot/compressed/head_64.S | 8 ++++++++ arch/x86/boot/compressed/pgtable.h | 2 +- 2 files changed, 9 insertions(+), 1 deletion(-) diff --git a/arch/x86/boot/compressed/head_64.S b/arch/x86/boot/compressed/head_64.S index 64037895b085..f105ae8651c9 100644 --- a/arch/x86/boot/compressed/head_64.S +++ b/arch/x86/boot/compressed/head_64.S @@ -600,6 +600,14 @@ ENTRY(trampoline_32bit_src) leal TRAMPOLINE_32BIT_PGTABLE_OFFSET(%ecx), %eax movl %eax, %cr3 3: + /* Set EFER.LME=1 as a precaution in case hypervsior pulls the rug */ + pushl %ecx + movl $MSR_EFER, %ecx + rdmsr + btsl $_EFER_LME, %eax + wrmsr + popl %ecx + /* Enable PAE and LA57 (if required) paging modes */ movl $X86_CR4_PAE, %eax cmpl $0, %edx diff --git a/arch/x86/boot/compressed/pgtable.h b/arch/x86/boot/compressed/pgtable.h index 91f75638f6e6..6ff7e81b5628 100644 --- a/arch/x86/boot/compressed/pgtable.h +++ b/arch/x86/boot/compressed/pgtable.h @@ -6,7 +6,7 @@ #define TRAMPOLINE_32BIT_PGTABLE_OFFSET 0 #define TRAMPOLINE_32BIT_CODE_OFFSET PAGE_SIZE -#define TRAMPOLINE_32BIT_CODE_SIZE 0x60 +#define TRAMPOLINE_32BIT_CODE_SIZE 0x70 #define TRAMPOLINE_32BIT_STACK_END TRAMPOLINE_32BIT_SIZE ^ permalink raw reply related [flat|nested] 4+ messages in thread
end of thread, other threads:[~2019-01-29 21:04 UTC | newest]
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2019-01-07 20:03 ` [PATCH 1/1] x86/boot/compressed/64: Set EFER.LME=1 in 32-bit trampoline code before returning to long mode Wei Huang
2019-01-07 21:53 ` Benjamin Gilbert
2019-01-07 22:02 ` Wei Huang
2019-01-29 21:03 ` [tip:x86/urgent] x86/boot/compressed/64: Set EFER.LME=1 in 32-bit trampoline " tip-bot for Wei Huang
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