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Message-ID: <59f698cf899db7eecb9838069401161a06dad7b4.camel@infradead.org>
Date: Fri, 02 Aug 2024 17:06:17 +0100
From: David Woodhouse <dwmw2@...radead.org>
To: Carsten Stollmaier <stollmc@...zon.com>, Sean Christopherson
<seanjc@...gle.com>, Paolo Bonzini <pbonzini@...hat.com>, Thomas Gleixner
<tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>, Borislav Petkov
<bp@...en8.de>, Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
"H. Peter Anvin" <hpa@...or.com>
Cc: nh-open-source@...zon.com, Peter Xu <peterx@...hat.com>, Sebastian
Biemueller <sbiemue@...zon.de>, kvm@...r.kernel.org,
linux-kernel@...r.kernel.org, Matthew Wilcox <willy@...radead.org>, Andrew
Morton <akpm@...ux-foundation.org>, "linux-mm@...ck.org"
<linux-mm@...ck.org>
Subject: Re: [PATCH] KVM: x86: Use gfn_to_pfn_cache for steal_time
On Fri, 2024-08-02 at 13:03 +0100, David Woodhouse wrote:
>
> I'm actually tempted to make user access *interruptible* though, and
> either add copy_{from,to}_user_interruptible() or change the semantics
> of the existing ones (which I believe are already killable).
>
> That would require each architecture implementing interruptible
> exceptions, by doing an extable lookup before the retry. Not overly
> complex, but needs to be done for all architectures (although not at
> once; we could live with not-yet-done architectures just remaining
> killable).
>
> Thoughts?
Utterly untested, hasn't even built yet and would need some cleanup
(and better thoughts about how to indicate -EFAULT vs. -EINTR instead
of having the caller check signal_pending() for itself). But should
demonstrate what I was thinking, at least...
diff --git a/arch/x86/include/asm/asm.h b/arch/x86/include/asm/asm.h
index 2bec0c89a95c..854ccd5f2342 100644
--- a/arch/x86/include/asm/asm.h
+++ b/arch/x86/include/asm/asm.h
@@ -229,6 +229,9 @@ register unsigned long current_stack_pointer asm(_ASM_SP);
#define _ASM_EXTABLE_UA(from, to) \
_ASM_EXTABLE_TYPE(from, to, EX_TYPE_UACCESS)
+#define _ASM_EXTABLE_UA_INTR(from, to) \
+ _ASM_EXTABLE_TYPE(from, to, EX_TYPE_UACCESS_INTERRUPTIBLE)
+
#define _ASM_EXTABLE_FAULT(from, to) \
_ASM_EXTABLE_TYPE(from, to, EX_TYPE_FAULT)
diff --git a/arch/x86/include/asm/extable_fixup_types.h b/arch/x86/include/asm/extable_fixup_types.h
index 906b0d5541e8..651d42f39e9b 100644
--- a/arch/x86/include/asm/extable_fixup_types.h
+++ b/arch/x86/include/asm/extable_fixup_types.h
@@ -36,7 +36,7 @@
#define EX_TYPE_DEFAULT 1
#define EX_TYPE_FAULT 2
#define EX_TYPE_UACCESS 3
-/* unused, was: #define EX_TYPE_COPY 4 */
+#define EX_TYPE_UACCESS_INTERRUPTIBLE 4
#define EX_TYPE_CLEAR_FS 5
#define EX_TYPE_FPU_RESTORE 6
#define EX_TYPE_BPF 7
diff --git a/arch/x86/include/asm/trapnr.h b/arch/x86/include/asm/trapnr.h
index 8d1154cdf787..9f6397bad398 100644
--- a/arch/x86/include/asm/trapnr.h
+++ b/arch/x86/include/asm/trapnr.h
@@ -41,4 +41,5 @@
#define X86_TRAP_VC 29 /* VMM Communication Exception */
#define X86_TRAP_IRET 32 /* IRET Exception */
+#define X86_TRAP_INTERRUPTIBLE 0x40000000 /* Internal, for interruptible exceptions */
#endif
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index cef729a25655..ab00150d360b 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -3819,12 +3819,15 @@ static void record_steal_time(struct kvm_vcpu *vcpu)
asm volatile("1: xchgb %0, %2\n"
"xor %1, %1\n"
"2:\n"
- _ASM_EXTABLE_UA(1b, 2b)
+ _ASM_EXTABLE_UA_INTR(1b, 2b)
: "+q" (st_preempted),
"+&r" (err),
"+m" (st->preempted));
- if (err)
+ if (err) {
+ if (signal_pending(current))
+ err = -EINTR;
goto out;
+ }
user_access_end();
diff --git a/arch/x86/mm/extable.c b/arch/x86/mm/extable.c
index 51986e8a9d35..d2cef84042a5 100644
--- a/arch/x86/mm/extable.c
+++ b/arch/x86/mm/extable.c
@@ -325,6 +325,12 @@ int fixup_exception(struct pt_regs *regs, int trapnr, unsigned long error_code,
reg = FIELD_GET(EX_DATA_REG_MASK, e->data);
imm = FIELD_GET(EX_DATA_IMM_MASK, e->data);
+ if (trapnr & X86_TRAP_INTERRUPTIBLE) {
+ trapnr &= ~X86_TRAP_INTERRUPTIBLE;
+ if (type != EX_TYPE_UACCESS_INTERRUPTIBLE)
+ return 0;
+ }
+
switch (type) {
case EX_TYPE_DEFAULT:
case EX_TYPE_DEFAULT_MCE_SAFE:
@@ -333,6 +339,7 @@ int fixup_exception(struct pt_regs *regs, int trapnr, unsigned long error_code,
case EX_TYPE_FAULT_MCE_SAFE:
return ex_handler_fault(e, regs, trapnr);
case EX_TYPE_UACCESS:
+ case EX_TYPE_UACCESS_INTERRUPTIBLE:
return ex_handler_uaccess(e, regs, trapnr, fault_addr);
case EX_TYPE_CLEAR_FS:
return ex_handler_clear_fs(e, regs);
diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c
index e6c469b323cc..4b32348dbb23 100644
--- a/arch/x86/mm/fault.c
+++ b/arch/x86/mm/fault.c
@@ -1388,18 +1388,6 @@ void do_user_addr_fault(struct pt_regs *regs,
*/
fault = handle_mm_fault(vma, address, flags, regs);
- if (fault_signal_pending(fault, regs)) {
- /*
- * Quick path to respond to signals. The core mm code
- * has unlocked the mm for us if we get here.
- */
- if (!user_mode(regs))
- kernelmode_fixup_or_oops(regs, error_code, address,
- SIGBUS, BUS_ADRERR,
- ARCH_DEFAULT_PKEY);
- return;
- }
-
/* The fault is fully completed (including releasing mmap lock) */
if (fault & VM_FAULT_COMPLETED)
return;
@@ -1410,6 +1398,28 @@ void do_user_addr_fault(struct pt_regs *regs,
* that we made any progress. Handle this case first.
*/
if (unlikely(fault & VM_FAULT_RETRY)) {
+ if (signal_pending(current)) {
+ if (user_mode(regs))
+ return;
+
+ if (fatal_signal_pending(current)) {
+ kernelmode_fixup_or_oops(regs, error_code, address,
+ SIGBUS, BUS_ADRERR,
+ ARCH_DEFAULT_PKEY);
+ return;
+ }
+
+ /*
+ * First time round, if woken by a signal, see if there
+ * is an interruptible exception handler. If so, do it.
+ * Else, switch off FAULT_FLAG_INTERRUPTIBLE.
+ */
+ if (fixup_exception(regs, X86_TRAP_INTERRUPTIBLE | X86_TRAP_PF,
+ error_code, address))
+ return;
+ flags &= ~FAULT_FLAG_INTERRUPTIBLE;
+ }
+
flags |= FAULT_FLAG_TRIED;
goto retry;
}
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