From 93de2a6a4b91b72607136dd656edf03fb399d27f Mon Sep 17 00:00:00 2001 From: Sean Christopherson Date: Wed, 23 Sep 2026 09:37:21 -0700 Subject: KVM: SEV: Do cache maintenance on the source VM during intra-host migration Manually perform cache maintenance on the source VM during intra-host migration to ensure no stale data is left in CPU caches after the VM is destroyed. Because the source VM is "converted" to a non-SEV VM, KVM's memory reclaim flows won't trigger cache maintenance, e.g. when all guest memory is reclaimed in response to detaching from the mmu_notifier. Note, relying on the destination VM to do cache maintenance isn't an option as KVM doesn't require identical guest memory configurations, i.e. the source VM may have access to memory that the destination VM does not. Enforcing equivalent memory configurations is infeasible, as it would require a *deep* comparison of memslots, e.g. to verify that not only are the memslot identical, but what the memslots point at is also identical. Fixes: b56639318bb2 ("KVM: SEV: Add support for SEV intra host migration") Cc: stable@vger.kernel.org Reported-by: Stefan Teodorescu Signed-off-by: Sean Christopherson Message-ID: <20260923163721.1584779-3-seanjc@google.com> Signed-off-by: Paolo Bonzini --- arch/alpha/lib/divide.S | 199 ++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 199 insertions(+) create mode 100644 arch/alpha/lib/divide.S (limited to 'arch/alpha/lib/divide.S') diff --git a/arch/alpha/lib/divide.S b/arch/alpha/lib/divide.S new file mode 100644 index 000000000..db01840d7 --- /dev/null +++ b/arch/alpha/lib/divide.S @@ -0,0 +1,199 @@ +/* SPDX-License-Identifier: GPL-2.0 */ +/* + * arch/alpha/lib/divide.S + * + * (C) 1995 Linus Torvalds + * + * Alpha division.. + */ + +/* + * The alpha chip doesn't provide hardware division, so we have to do it + * by hand. The compiler expects the functions + * + * __divqu: 64-bit unsigned long divide + * __remqu: 64-bit unsigned long remainder + * __divqs/__remqs: signed 64-bit + * __divlu/__remlu: unsigned 32-bit + * __divls/__remls: signed 32-bit + * + * These are not normal C functions: instead of the normal + * calling sequence, these expect their arguments in registers + * $24 and $25, and return the result in $27. Register $28 may + * be clobbered (assembly temporary), anything else must be saved. + * + * In short: painful. + * + * This is a rather simple bit-at-a-time algorithm: it's very good + * at dividing random 64-bit numbers, but the more usual case where + * the divisor is small is handled better by the DEC algorithm + * using lookup tables. This uses much less memory, though, and is + * nicer on the cache.. Besides, I don't know the copyright status + * of the DEC code. + */ + +/* + * My temporaries: + * $0 - current bit + * $1 - shifted divisor + * $2 - modulus/quotient + * + * $23 - return address + * $24 - dividend + * $25 - divisor + * + * $27 - quotient/modulus + * $28 - compare status + */ + +#include +#define halt .long 0 + +/* + * Select function type and registers + */ +#define mask $0 +#define divisor $1 +#define compare $28 +#define tmp1 $3 +#define tmp2 $4 + +#ifdef DIV +#define DIV_ONLY(x,y...) x,##y +#define MOD_ONLY(x,y...) +#define func(x) __div##x +#define modulus $2 +#define quotient $27 +#define GETSIGN(x) xor $24,$25,x +#define STACK 48 +#else +#define DIV_ONLY(x,y...) +#define MOD_ONLY(x,y...) x,##y +#define func(x) __rem##x +#define modulus $27 +#define quotient $2 +#define GETSIGN(x) bis $24,$24,x +#define STACK 32 +#endif + +/* + * For 32-bit operations, we need to extend to 64-bit + */ +#ifdef INTSIZE +#define ufunction func(lu) +#define sfunction func(l) +#define LONGIFY(x) zapnot x,15,x +#define SLONGIFY(x) addl x,0,x +#else +#define ufunction func(qu) +#define sfunction func(q) +#define LONGIFY(x) +#define SLONGIFY(x) +#endif + +.set noat +.align 3 +.globl ufunction +.ent ufunction +ufunction: + subq $30,STACK,$30 + .frame $30,STACK,$23 + .prologue 0 + +7: stq $1, 0($30) + bis $25,$25,divisor + stq $2, 8($30) + bis $24,$24,modulus + stq $0,16($30) + bis $31,$31,quotient + LONGIFY(divisor) + stq tmp1,24($30) + LONGIFY(modulus) + bis $31,1,mask + DIV_ONLY(stq tmp2,32($30)) + beq divisor, 9f /* div by zero */ + +#ifdef INTSIZE + /* + * shift divisor left, using 3-bit shifts for + * 32-bit divides as we can't overflow. Three-bit + * shifts will result in looping three times less + * here, but can result in two loops more later. + * Thus using a large shift isn't worth it (and + * s8add pairs better than a sll..) + */ +1: cmpult divisor,modulus,compare + s8addq divisor,$31,divisor + s8addq mask,$31,mask + bne compare,1b +#else +1: cmpult divisor,modulus,compare + blt divisor, 2f + addq divisor,divisor,divisor + addq mask,mask,mask + bne compare,1b + unop +#endif + + /* ok, start to go right again.. */ +2: DIV_ONLY(addq quotient,mask,tmp2) + srl mask,1,mask + cmpule divisor,modulus,compare + subq modulus,divisor,tmp1 + DIV_ONLY(cmovne compare,tmp2,quotient) + srl divisor,1,divisor + cmovne compare,tmp1,modulus + bne mask,2b + +9: ldq $1, 0($30) + ldq $2, 8($30) + ldq $0,16($30) + ldq tmp1,24($30) + DIV_ONLY(ldq tmp2,32($30)) + addq $30,STACK,$30 + ret $31,($23),1 + .end ufunction +EXPORT_SYMBOL(ufunction) + +/* + * Uhh.. Ugly signed division. I'd rather not have it at all, but + * it's needed in some circumstances. There are different ways to + * handle this, really. This does: + * -a / b = a / -b = -(a / b) + * -a % b = -(a % b) + * a % -b = a % b + * which is probably not the best solution, but at least should + * have the property that (x/y)*y + (x%y) = x. + */ +.align 3 +.globl sfunction +.ent sfunction +sfunction: + subq $30,STACK,$30 + .frame $30,STACK,$23 + .prologue 0 + bis $24,$25,$28 + SLONGIFY($28) + bge $28,7b + stq $24,0($30) + subq $31,$24,$28 + stq $25,8($30) + cmovlt $24,$28,$24 /* abs($24) */ + stq $23,16($30) + subq $31,$25,$28 + stq tmp1,24($30) + cmovlt $25,$28,$25 /* abs($25) */ + unop + bsr $23,ufunction + ldq $24,0($30) + ldq $25,8($30) + GETSIGN($28) + subq $31,$27,tmp1 + SLONGIFY($28) + ldq $23,16($30) + cmovlt $28,tmp1,$27 + ldq tmp1,24($30) + addq $30,STACK,$30 + ret $31,($23),1 + .end sfunction +EXPORT_SYMBOL(sfunction) -- cgit v1.3.1